diff --git a/HISTORY.md b/HISTORY.md
index 8c5d78e1f..da104c5d8 100644
--- a/HISTORY.md
+++ b/HISTORY.md
@@ -2,8 +2,10 @@
 https://github.com/josdejong/mathjs
 
 
-## not yet released, version 0.19.1
+## not yet released, version 0.20.0
 
+- Switched to module `decimal.js` for BigNumber support, instead of
+  `bignumber.js`.
 - Implemented conditional operator `a ? b : c` in expression parser.
 - Improved function `ifElse`, is now specified for special data types too.
 - Minor bug fixes.
diff --git a/docs/configuration.md b/docs/configuration.md
index eb7da5f40..bcecc4303 100644
--- a/docs/configuration.md
+++ b/docs/configuration.md
@@ -16,19 +16,14 @@ Available configuration settings are:
   like `eval `which cannot determine the correct type of output from the
   functions input. For most functions though, the type of output is determined
   from the the input: a number as input will return a number as output,
-  a bignumber as input returns a bignumber as output.
+  a BigNumber as input returns a BigNumber as output.
   Available values are: `'number'` (default) or `'bignumber'`.
-  Big numbers have higher precision than the default numbers of JavaScript.
+  BigNumbers have higher precision than the default numbers of JavaScript.
 
 - `decimals`. The maximum number of decimal places behind the decimal
-  point (not the number of significant digits). Only applies to big numbers,
+  point (not the number of significant digits). Only applies to BigNumbers,
   not to numbers. Default value is 20.
 
-  *Important: This setting is applied application wide to all BigNumbers.
-  Behind the scenes, this setting is applied as the global `DECIMAL_PLACES`
-  setting of the [bignumber.js](https://github.com/MikeMcl/bignumber.js)
-  library used by math.js.*
-
 
 ## Examples
 
@@ -72,13 +67,13 @@ math2.config({
 math2.range(0, 4); // Matrix [0, 1, 2, 3]
 ```
 
-### Configuration for big numbers
+### Configuration for BigNumbers
 
 ```js
 // load the library
 var mathjs = require('mathjs');
 
-// use big numbers by default
+// use BigNumbers by default
 var math3 = mathjs({
   number: 'bignumber',
   decimals: 32
diff --git a/docs/datatypes/bignumbers.md b/docs/datatypes/bignumbers.md
index 07b6537f6..7f8c015ef 100644
--- a/docs/datatypes/bignumbers.md
+++ b/docs/datatypes/bignumbers.md
@@ -1,33 +1,36 @@
-# Big Numbers
+# BigNumbers
 
-For calculations with an arbitrary precision, math.js supports BigNumber.
-BigNumber is powered by the the library
-[bignumber.js](https://github.com/MikeMcl/bignumber.js/).
+For calculations with an arbitrary precision, math.js supports a `BigNumber`
+data type. BigNumber support is powered by
+[decimal.js](https://github.com/MikeMcl/decimal.js/).
 
-A big number can be created using the function `bignumber`:
+A BigNumber can be created using the function `bignumber`:
 
 ```js
 math.bignumber('2.3e+500'); // BigNumber, 2.3e+500
 ```
 
 Most functions can determine the type of output from the type of input:
-a number as input will return a number as output, a bignumber as input returns
-a bignumber as output. Functions which cannot determine the type of output
+a number as input will return a number as output, a BigNumber as input returns
+a BigNumber as output. Functions which cannot determine the type of output
 from the input (for example `math.eval`) use the default number type `number`,
-which can be configured when instantiating math.js. To configure the use of big
-numbers instead of [numbers](numbers.md) by default, configure math.js like:
+which can be configured when instantiating math.js. To configure the use of
+BigNumbers instead of [numbers](numbers.md) by default, configure math.js like:
 
 ```js
 var mathjs = require('mathjs'),
     math = mathjs({
       number: 'bignumber', // Default type of number: 'number' (default) or 'bignumber'
-      decimals: 20         // Number decimal places behind the dot for big numbers
+      decimals: 20         // Number of decimal places behind the dot for BigNumbers
     });
 
 // use math
 math.eval('0.1 + 0.2'); // BigNumber, 0.3
 ```
 
+The default precision for BigNumber is 20 digits, and can be configured with
+the option `decimals`.
+
 *Important:
 BigNumber is not supported by the following functions:
 exp, gcd, lcm, log, log10, xgcd,
@@ -45,29 +48,18 @@ precision, it is less likely that round-off errors occur:
 math.add(0.1, 0.2);                                     // Number, 0.30000000000000004
 math.divide(0.3, 0.2);                                  // Number, 1.4999999999999998
 
-// no round-off errors with big numbers :)
+// no round-off errors with BigNumbers :)
 math.add(math.bignumber(0.1), math.bignumber(0.2));     // BigNumber, 0.3
 math.divide(math.bignumber(0.3), math.bignumber(0.2));  // BigNumber, 1.5
 ```
 
-The default precision for BigNumber is 20 digits. This is a global setting
-in the [underlying BigNumber library](https://github.com/MikeMcl/bignumber.js/),
-which can be changed by configuring BigNumber:
-
-```js
-BigNumber.config({DECIMAL_PLACES: 32});
-```
-
-*Important: To work with small numbers, `DECIMAL_PLACES` must be configured
-sufficiently large.*
-
-Big numbers can be converted to numbers and vice versa using the functions
+BigNumbers can be converted to numbers and vice versa using the functions
 `number` and `bignumber`. When converting a BigNumber to a Number, the high
 precision of the BigNumber will be lost. When a BigNumber is too large to be represented
 as Number, it will be initialized as `Infinity`.
 
 ```js
-// converting numbers and bignumbers
+// converting numbers and BigNumbers
 var a = math.number(0.3);                         // Number, 0.3
 var b = math.bignumber(a);                        // BigNumber, 0.3
 var c = math.number(b);                           // Number, 0.3
diff --git a/docs/datatypes/index.md b/docs/datatypes/index.md
index 72509ea9e..13e5b64c7 100644
--- a/docs/datatypes/index.md
+++ b/docs/datatypes/index.md
@@ -24,7 +24,7 @@ math.subtract(7.1, 2.3);        // 4.8
 math.round(math.pi, 3);         // 3.142
 math.sqrt(4.41e2);              // 21
 
-// use big numbers
+// use BigNumbers
 math.add(math.bignumber(0.1), math.bignumber(0.2)); // BigNumber, 0.3
 
 // use strings
diff --git a/docs/datatypes/numbers.md b/docs/datatypes/numbers.md
index d734e9339..256d0fdb3 100644
--- a/docs/datatypes/numbers.md
+++ b/docs/datatypes/numbers.md
@@ -4,11 +4,11 @@ Math.js supports two types of numbers:
 
 - Number for fast floating point arithmetic, described on this page.
 - BigNumber for arbitrary precision arithmetic, describe on the page
-  [Big Numbers](bignumbers.md).
+  [BigNumbers](bignumbers.md).
 
 Most functions can determine the type of output from the type of input:
-a number as input will return a number as output, a bignumber as input returns
-a bignumber as output. Functions which cannot determine the type of output
+a number as input will return a number as output, a BigNumber as input returns
+a BigNumber as output. Functions which cannot determine the type of output
 from the input (for example `math.eval`) use the default number type, which
 can be configured when instantiating math.js:
 
diff --git a/docs/expressions.md b/docs/expressions.md
index 57eb6925a..db839eb96 100644
--- a/docs/expressions.md
+++ b/docs/expressions.md
@@ -456,9 +456,9 @@ math.format(ans, {precision: 14});  // "0.3"
 ```
 
 
-#### Big numbers
+#### BigNumbers
 
-Math.js supports big numbers for calculations with an arbitrary precision.
+Math.js supports BigNumbers for calculations with an arbitrary precision.
 The pros and cons of Number and BigNumber are explained in detail on the page
 [Numbers](datatypes/numbers.md).
 
@@ -484,7 +484,7 @@ var mathjs = require('mathjs'),
 math.eval('0.1 + 0.2'); // BigNumber, 0.3
 ```
 
-Big numbers can be converted to numbers and vice versa using the functions
+BigNumbers can be converted to numbers and vice versa using the functions
 `number` and `bignumber`. When converting a BigNumber to a Number, the high
 precision of the BigNumber will be lost. When a BigNumber is too large to be represented
 as Number, it will be initialized as `Infinity`.
diff --git a/docs/index.md b/docs/index.md
index 5460b93cc..b26e6a95a 100644
--- a/docs/index.md
+++ b/docs/index.md
@@ -7,7 +7,7 @@
 - [Chained Operations](chained_operations.md)
 - [Data Types](datatypes/index.md)
   - [Numbers](datatypes/numbers.md)
-  - [Big Numbers](datatypes/bignumbers.md)
+  - [BigNumbers](datatypes/bignumbers.md)
   - [Complex Numbers](datatypes/complex_numbers.md)
   - [Matrices](datatypes/matrices.md)
   - [Units](datatypes/units.md)
diff --git a/examples/bignumbers.js b/examples/bignumbers.js
index e5f2a5725..a163657e0 100644
--- a/examples/bignumbers.js
+++ b/examples/bignumbers.js
@@ -1,11 +1,11 @@
-// big numbers
+// BigNumbers
 
 // load math.js and create an instance
-// the default type of numbers is configured as big numbers
+// the default type of numbers is configured as BigNumbers
 var mathjs = require('../index'),
     math = mathjs({
       number: 'bignumber',  // Default type of number: 'number' (default) or 'bignumber'
-      decimals: 20          // number decimal places behind the dot for big numbers
+      decimals: 20          // number of decimal places behind the dot for BigNumbers
     });
 
 /**
@@ -21,19 +21,19 @@ print(math.add(0.1, 0.2));    // Number, 0.30000000000000004
 print(math.divide(0.3, 0.2)); // Number, 1.4999999999999998
 console.log();
 
-console.log('no round-off errors with big numbers');
+console.log('no round-off errors with BigNumbers');
 print(math.add(math.bignumber(0.1), math.bignumber(0.2)));     // BigNumber, 0.3
 print(math.divide(math.bignumber(0.3), math.bignumber(0.2)));  // BigNumber, 1.5
 console.log();
 
-console.log('create big numbers from strings when exceeding the range of a number');
+console.log('create BigNumbers from strings when exceeding the range of a number');
 print(math.bignumber(1.2e+500));    // BigNumber, Infinity      WRONG
 print(math.bignumber('1.2e+500'));  // BigNumber, 1.2e+500
 console.log();
 
-// one can work conveniently with big numbers using the expression parser.
-// note though that big numbers are only supported in arithmetic functions
-console.log('use big numbers in the expression parser');
+// one can work conveniently with BigNumbers using the expression parser.
+// note though that BigNumbers are only supported in arithmetic functions
+console.log('use BigNumbers in the expression parser');
 print(math.eval('0.1 + 0.2'));  // BigNumber, 0.3
 print(math.eval('0.3 / 0.2'));  // BigNumber, 1.5
 console.log();
diff --git a/lib/expression/node/ConstantNode.js b/lib/expression/node/ConstantNode.js
index 51dd0ceae..261081516 100644
--- a/lib/expression/node/ConstantNode.js
+++ b/lib/expression/node/ConstantNode.js
@@ -1,6 +1,6 @@
 var Node = require('./Node'),
     Complex = require('../../type/Complex'),
-    BigNumber = require('bignumber.js'),
+    BigNumber = require('../../type/BigNumber'),
     string = require('../../util/string'),
     isString = string.isString;
 
diff --git a/lib/expression/node/IndexNode.js b/lib/expression/node/IndexNode.js
index 837c85f81..0c9f642b1 100644
--- a/lib/expression/node/IndexNode.js
+++ b/lib/expression/node/IndexNode.js
@@ -1,12 +1,12 @@
-var number= require('../../util/number.js'),
+var number= require('../../util/number'),
 
     Node = require('./Node.js'),
-    RangeNode = require('./RangeNode.js'),
-    SymbolNode = require('./SymbolNode.js'),
+    RangeNode = require('./RangeNode'),
+    SymbolNode = require('./SymbolNode'),
 
-    BigNumber = require('bignumber.js'),
-    Index = require('../../type/Index.js'),
-    Range = require('../../type/Range.js'),
+    BigNumber = require('../../type/BigNumber'),
+    Index = require('../../type/Index'),
+    Range = require('../../type/Range'),
 
     isNumber = number.isNumber,
     toNumber = number.toNumber,
diff --git a/lib/expression/node/ParamsNode.js b/lib/expression/node/ParamsNode.js
index be1481925..aabb92a73 100644
--- a/lib/expression/node/ParamsNode.js
+++ b/lib/expression/node/ParamsNode.js
@@ -4,7 +4,7 @@ var number= require('../../util/number'),
     RangeNode = require('./RangeNode'),
     SymbolNode = require('./SymbolNode'),
 
-    BigNumber = require('bignumber.js'),
+    BigNumber = require('../../type/BigNumber'),
     Index = require('../../type/Index'),
     Range = require('../../type/Range'),
 
diff --git a/lib/expression/node/RangeNode.js b/lib/expression/node/RangeNode.js
index befea2fc0..84561150f 100644
--- a/lib/expression/node/RangeNode.js
+++ b/lib/expression/node/RangeNode.js
@@ -1,7 +1,7 @@
 var number = require('../../util/number'),
     Node = require('./Node'),
 
-    BigNumber = require('bignumber.js'),
+    BigNumber = require('../../type/BigNumber'),
     Range = require('../../type/Range'),
     Matrix = require('../../type/Matrix'),
 
diff --git a/lib/expression/node/UnitNode.js b/lib/expression/node/UnitNode.js
index a0533deb2..145179e92 100644
--- a/lib/expression/node/UnitNode.js
+++ b/lib/expression/node/UnitNode.js
@@ -1,6 +1,6 @@
 var Node = require('./Node'),
 
-    BigNumber = require('bignumber.js'),
+    BigNumber = require('../../type/BigNumber'),
     Complex = require('../../type/Complex'),
     Unit = require('../../type/Unit'),
 
diff --git a/lib/expression/node/UpdateNode.js b/lib/expression/node/UpdateNode.js
index 1b8cdca8d..b6c942ea2 100644
--- a/lib/expression/node/UpdateNode.js
+++ b/lib/expression/node/UpdateNode.js
@@ -5,7 +5,7 @@ var number= require('../../util/number'),
     IndexNode = require('./IndexNode'),
     SymbolNode = require('./SymbolNode'),
 
-    BigNumber = require('bignumber.js'),
+    BigNumber = require('../../type/BigNumber'),
     Index = require('../../type/Index'),
     Range = require('../../type/Range'),
 
diff --git a/lib/function/arithmetic/abs.js b/lib/function/arithmetic/abs.js
index 92714cbee..91129d3da 100644
--- a/lib/function/arithmetic/abs.js
+++ b/lib/function/arithmetic/abs.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       Matrix = require('../../type/Matrix'),
       collection = require('../../type/collection'),
diff --git a/lib/function/arithmetic/add.js b/lib/function/arithmetic/add.js
index 46e2a743a..4be5bf42c 100644
--- a/lib/function/arithmetic/add.js
+++ b/lib/function/arithmetic/add.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       Matrix = require('../../type/Matrix'),
       Unit = require('../../type/Unit'),
diff --git a/lib/function/arithmetic/ceil.js b/lib/function/arithmetic/ceil.js
index daf5b7106..8e8c9890a 100644
--- a/lib/function/arithmetic/ceil.js
+++ b/lib/function/arithmetic/ceil.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       collection = require('../../type/collection'),
 
diff --git a/lib/function/arithmetic/compare.js b/lib/function/arithmetic/compare.js
index dc3524bb6..935ef66aa 100644
--- a/lib/function/arithmetic/compare.js
+++ b/lib/function/arithmetic/compare.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       Unit = require('../../type/Unit'),
       collection = require('../../type/collection'),
diff --git a/lib/function/arithmetic/cube.js b/lib/function/arithmetic/cube.js
index bb8b37b2b..9dd048b64 100644
--- a/lib/function/arithmetic/cube.js
+++ b/lib/function/arithmetic/cube.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       collection = require('../../type/collection'),
 
diff --git a/lib/function/arithmetic/divide.js b/lib/function/arithmetic/divide.js
index 9cec46cab..9bb7fe5cd 100644
--- a/lib/function/arithmetic/divide.js
+++ b/lib/function/arithmetic/divide.js
@@ -1,7 +1,7 @@
 module.exports = function(math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       Matrix = require('../../type/Matrix'),
       Unit = require('../../type/Unit'),
diff --git a/lib/function/arithmetic/equal.js b/lib/function/arithmetic/equal.js
index 933763998..cfb13811d 100644
--- a/lib/function/arithmetic/equal.js
+++ b/lib/function/arithmetic/equal.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       Unit = require('../../type/Unit'),
       collection = require('../../type/collection'),
diff --git a/lib/function/arithmetic/exp.js b/lib/function/arithmetic/exp.js
index 4697e89d8..9bde185b9 100644
--- a/lib/function/arithmetic/exp.js
+++ b/lib/function/arithmetic/exp.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       Matrix = require('../../type/Matrix'),
       collection = require('../../type/collection'),
diff --git a/lib/function/arithmetic/fix.js b/lib/function/arithmetic/fix.js
index 11a9f9067..54a8e7fb8 100644
--- a/lib/function/arithmetic/fix.js
+++ b/lib/function/arithmetic/fix.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       collection = require('../../type/collection'),
 
diff --git a/lib/function/arithmetic/floor.js b/lib/function/arithmetic/floor.js
index 6028d4b39..83e00b3e2 100644
--- a/lib/function/arithmetic/floor.js
+++ b/lib/function/arithmetic/floor.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       collection = require('../../type/collection'),
 
diff --git a/lib/function/arithmetic/gcd.js b/lib/function/arithmetic/gcd.js
index 34a03603d..1f5b4a886 100644
--- a/lib/function/arithmetic/gcd.js
+++ b/lib/function/arithmetic/gcd.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       collection = require('../../type/collection'),
 
       isNumber = util.number.isNumber,
diff --git a/lib/function/arithmetic/larger.js b/lib/function/arithmetic/larger.js
index 899f1e533..314a49421 100644
--- a/lib/function/arithmetic/larger.js
+++ b/lib/function/arithmetic/larger.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       Unit = require('../../type/Unit'),
       collection = require('../../type/collection'),
diff --git a/lib/function/arithmetic/largereq.js b/lib/function/arithmetic/largereq.js
index a88263002..82ca9cac9 100644
--- a/lib/function/arithmetic/largereq.js
+++ b/lib/function/arithmetic/largereq.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       Unit = require('../../type/Unit'),
       collection = require('../../type/collection'),
diff --git a/lib/function/arithmetic/lcm.js b/lib/function/arithmetic/lcm.js
index 31f2e273c..22438bd6f 100644
--- a/lib/function/arithmetic/lcm.js
+++ b/lib/function/arithmetic/lcm.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       collection = require('../../type/collection'),
 
       isNumber = util.number.isNumber,
diff --git a/lib/function/arithmetic/log.js b/lib/function/arithmetic/log.js
index d881c6990..f84f81bdf 100644
--- a/lib/function/arithmetic/log.js
+++ b/lib/function/arithmetic/log.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       collection = require('../../type/collection'),
 
diff --git a/lib/function/arithmetic/log10.js b/lib/function/arithmetic/log10.js
index 9d4b31cc8..916a1c1de 100644
--- a/lib/function/arithmetic/log10.js
+++ b/lib/function/arithmetic/log10.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       collection = require('../../type/collection'),
 
diff --git a/lib/function/arithmetic/mod.js b/lib/function/arithmetic/mod.js
index 4c6a18d82..f1cadaef0 100644
--- a/lib/function/arithmetic/mod.js
+++ b/lib/function/arithmetic/mod.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       collection = require('../../type/collection'),
 
       isNumber = util.number.isNumber,
diff --git a/lib/function/arithmetic/multiply.js b/lib/function/arithmetic/multiply.js
index 428bc49ba..5ede71f12 100644
--- a/lib/function/arithmetic/multiply.js
+++ b/lib/function/arithmetic/multiply.js
@@ -1,7 +1,7 @@
 module.exports = function(math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       Matrix = require('../../type/Matrix'),
       Unit = require('../../type/Unit'),
diff --git a/lib/function/arithmetic/pow.js b/lib/function/arithmetic/pow.js
index d1d7ebc06..a6f9b2987 100644
--- a/lib/function/arithmetic/pow.js
+++ b/lib/function/arithmetic/pow.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       Matrix = require('../../type/Matrix'),
       collection = require('../../type/collection'),
diff --git a/lib/function/arithmetic/round.js b/lib/function/arithmetic/round.js
index 61be56258..f9894dc2e 100644
--- a/lib/function/arithmetic/round.js
+++ b/lib/function/arithmetic/round.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       collection = require('../../type/collection'),
 
@@ -43,7 +43,7 @@ module.exports = function (math) {
       }
 
       if (x instanceof BigNumber) {
-        return x.round();
+        return x.toDecimalPlaces(0);
       }
 
       if (isCollection(x)) {
@@ -85,7 +85,7 @@ module.exports = function (math) {
       }
 
       if (x instanceof BigNumber) {
-        return x.round(n);
+        return x.toDecimalPlaces(n);
       }
 
       if (isCollection(x) || isCollection(n)) {
diff --git a/lib/function/arithmetic/sign.js b/lib/function/arithmetic/sign.js
index 518bdb3f8..5333fc7b9 100644
--- a/lib/function/arithmetic/sign.js
+++ b/lib/function/arithmetic/sign.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       collection = require('../../type/collection'),
 
diff --git a/lib/function/arithmetic/smaller.js b/lib/function/arithmetic/smaller.js
index 1c1cfe036..c1ef6648d 100644
--- a/lib/function/arithmetic/smaller.js
+++ b/lib/function/arithmetic/smaller.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       Unit = require('../../type/Unit'),
       collection = require('../../type/collection'),
diff --git a/lib/function/arithmetic/smallereq.js b/lib/function/arithmetic/smallereq.js
index 223f62231..436847197 100644
--- a/lib/function/arithmetic/smallereq.js
+++ b/lib/function/arithmetic/smallereq.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       Unit = require('../../type/Unit'),
       collection = require('../../type/collection'),
diff --git a/lib/function/arithmetic/sqrt.js b/lib/function/arithmetic/sqrt.js
index 2c5fc8831..7f7aa18c9 100644
--- a/lib/function/arithmetic/sqrt.js
+++ b/lib/function/arithmetic/sqrt.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       collection = require('../../type/collection'),
 
diff --git a/lib/function/arithmetic/square.js b/lib/function/arithmetic/square.js
index 603fb569e..1077682cb 100644
--- a/lib/function/arithmetic/square.js
+++ b/lib/function/arithmetic/square.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       collection = require('../../type/collection'),
 
diff --git a/lib/function/arithmetic/subtract.js b/lib/function/arithmetic/subtract.js
index 155d75845..e00cc2bc3 100644
--- a/lib/function/arithmetic/subtract.js
+++ b/lib/function/arithmetic/subtract.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       Matrix = require('../../type/Matrix'),
       Unit = require('../../type/Unit'),
diff --git a/lib/function/arithmetic/unary.js b/lib/function/arithmetic/unary.js
index 939f22208..a55be06aa 100644
--- a/lib/function/arithmetic/unary.js
+++ b/lib/function/arithmetic/unary.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       Unit = require('../../type/Unit'),
       collection = require('../../type/collection'),
diff --git a/lib/function/arithmetic/unequal.js b/lib/function/arithmetic/unequal.js
index d94507e7b..0c7c0c397 100644
--- a/lib/function/arithmetic/unequal.js
+++ b/lib/function/arithmetic/unequal.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       Unit = require('../../type/Unit'),
       collection = require('../../type/collection'),
diff --git a/lib/function/arithmetic/xgcd.js b/lib/function/arithmetic/xgcd.js
index 3f17f0877..d00c13506 100644
--- a/lib/function/arithmetic/xgcd.js
+++ b/lib/function/arithmetic/xgcd.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
 
       toNumber = util.number.toNumber,
       isNumber = util.number.isNumber,
diff --git a/lib/function/complex/arg.js b/lib/function/complex/arg.js
index 115671910..695cc1b78 100644
--- a/lib/function/complex/arg.js
+++ b/lib/function/complex/arg.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       collection = require('../../type/collection'),
 
diff --git a/lib/function/complex/conj.js b/lib/function/complex/conj.js
index be4b855a1..3d151a213 100644
--- a/lib/function/complex/conj.js
+++ b/lib/function/complex/conj.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       collection = require('../../type/collection'),
 
diff --git a/lib/function/complex/im.js b/lib/function/complex/im.js
index 6e8aa4bd3..a059e45fc 100644
--- a/lib/function/complex/im.js
+++ b/lib/function/complex/im.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       collection = require('../../type/collection'),
 
diff --git a/lib/function/complex/re.js b/lib/function/complex/re.js
index c16c8cd9f..37c6d3b0d 100644
--- a/lib/function/complex/re.js
+++ b/lib/function/complex/re.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       collection = require('../../type/collection'),
 
diff --git a/lib/function/construction/bignumber.js b/lib/function/construction/bignumber.js
index 0631d58f6..5e83f59c1 100644
--- a/lib/function/construction/bignumber.js
+++ b/lib/function/construction/bignumber.js
@@ -1,7 +1,8 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      // create a non-global instance of BigNumber
+      BigNumber = require('../../type/BigNumber'),
       collection = require('../../type/collection'),
 
       isCollection = collection.isCollection,
diff --git a/lib/function/construction/boolean.js b/lib/function/construction/boolean.js
index 12e95ed2e..62dd5ee68 100644
--- a/lib/function/construction/boolean.js
+++ b/lib/function/construction/boolean.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       collection = require('../../type/collection'),
 
       isCollection = collection.isCollection,
diff --git a/lib/function/construction/complex.js b/lib/function/construction/complex.js
index 74dafb0e3..4270e66f2 100644
--- a/lib/function/construction/complex.js
+++ b/lib/function/construction/complex.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       collection = require('../../type/collection'),
 
diff --git a/lib/function/construction/index.js b/lib/function/construction/index.js
index fd8d6b710..52da4ba4e 100644
--- a/lib/function/construction/index.js
+++ b/lib/function/construction/index.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Index = require('../../type/Index'),
 
       toNumber = util.number.toNumber;
diff --git a/lib/function/construction/number.js b/lib/function/construction/number.js
index 63f4c5933..a06cd2b29 100644
--- a/lib/function/construction/number.js
+++ b/lib/function/construction/number.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       collection = require('../../type/collection'),
 
       isCollection = collection.isCollection,
diff --git a/lib/function/construction/unit.js b/lib/function/construction/unit.js
index cfba18e68..585a192eb 100644
--- a/lib/function/construction/unit.js
+++ b/lib/function/construction/unit.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Unit = require('../../type/Unit'),
       collection = require('../../type/collection'),
 
diff --git a/lib/function/matrix/eye.js b/lib/function/matrix/eye.js
index dcc23c765..fc2090b30 100644
--- a/lib/function/matrix/eye.js
+++ b/lib/function/matrix/eye.js
@@ -1,7 +1,7 @@
 module.exports = function (math, settings) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Matrix = require('../../type/Matrix'),
       collection = require('../../type/collection'),
 
diff --git a/lib/function/matrix/ones.js b/lib/function/matrix/ones.js
index 2882c9af9..ade4aa3ea 100644
--- a/lib/function/matrix/ones.js
+++ b/lib/function/matrix/ones.js
@@ -1,7 +1,7 @@
 module.exports = function (math, settings) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Matrix = require('../../type/Matrix'),
       collection = require('../../type/collection'),
 
diff --git a/lib/function/matrix/range.js b/lib/function/matrix/range.js
index 456a38241..b5b45d645 100644
--- a/lib/function/matrix/range.js
+++ b/lib/function/matrix/range.js
@@ -1,7 +1,7 @@
 module.exports = function (math, settings) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Matrix = require('../../type/Matrix'),
       collection = require('../../type/collection'),
 
diff --git a/lib/function/matrix/resize.js b/lib/function/matrix/resize.js
index 6c01455a7..962867445 100644
--- a/lib/function/matrix/resize.js
+++ b/lib/function/matrix/resize.js
@@ -1,7 +1,7 @@
 module.exports = function (math, settings) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Matrix = require('../../type/Matrix'),
 
       array = util.array,
diff --git a/lib/function/matrix/size.js b/lib/function/matrix/size.js
index 75d21c69e..f7f323beb 100644
--- a/lib/function/matrix/size.js
+++ b/lib/function/matrix/size.js
@@ -1,7 +1,7 @@
 module.exports = function (math, settings) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       Unit = require('../../type/Unit'),
       Matrix = require('../../type/Matrix'),
diff --git a/lib/function/matrix/zeros.js b/lib/function/matrix/zeros.js
index dbddb0952..50c1eeb85 100644
--- a/lib/function/matrix/zeros.js
+++ b/lib/function/matrix/zeros.js
@@ -1,7 +1,7 @@
 module.exports = function (math, settings) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Matrix = require('../../type/Matrix'),
       collection = require('../../type/collection'),
 
diff --git a/lib/function/probability/combinations.js b/lib/function/probability/combinations.js
index 509aa18ae..69aee7a75 100644
--- a/lib/function/probability/combinations.js
+++ b/lib/function/probability/combinations.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       collection = require('../../type/collection'),
 
       isNumber = util.number.isNumber,
@@ -74,6 +74,6 @@ module.exports = function (math) {
    * @returns {boolean} isPositiveInteger
    */
   var isPositiveInteger = function(n) {
-    return n.round().equals(n) && n.gte(0);
+    return n.isInteger() && n.gte(0);
   };
 };
diff --git a/lib/function/probability/factorial.js b/lib/function/probability/factorial.js
index 96a8ef242..6b58b4ecc 100644
--- a/lib/function/probability/factorial.js
+++ b/lib/function/probability/factorial.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       collection = require('../../type/collection'),
 
       isNumber = util.number.isNumber,
@@ -85,6 +85,6 @@ module.exports = function (math) {
    * @returns {boolean} isPositiveInteger
    */
   var isPositiveInteger = function(n) {
-    return n.round().equals(n) && n.gte(0);
+    return n.isInteger() && n.gte(0);
   };
 };
diff --git a/lib/function/probability/permutations.js b/lib/function/probability/permutations.js
index 6ea976c30..def2d2a12 100644
--- a/lib/function/probability/permutations.js
+++ b/lib/function/probability/permutations.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
 
       isNumber = util.number.isNumber,
       isInteger = util.number.isInteger,
@@ -89,6 +89,6 @@ module.exports = function (math) {
    * @returns {boolean} isPositiveInteger
    */
   var isPositiveInteger = function(n) {
-    return n.round().equals(n) && n.gte(0);
+    return n.isInteger() && n.gte(0);
   };
 };
diff --git a/lib/function/statistics/median.js b/lib/function/statistics/median.js
index e9dc39770..f500ab918 100644
--- a/lib/function/statistics/median.js
+++ b/lib/function/statistics/median.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var Matrix = require('../../type/Matrix'),
       Unit = require('../../type/Unit'),
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       collection = require('../../type/collection'),
 
       isNumber = require('../../util/number').isNumber,
diff --git a/lib/function/statistics/var.js b/lib/function/statistics/var.js
index ae0605876..a4511fb1a 100644
--- a/lib/function/statistics/var.js
+++ b/lib/function/statistics/var.js
@@ -1,6 +1,6 @@
 module.exports = function (math) {
   var Matrix = require('../../type/Matrix'),
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       collection = require('../../type/collection'),
 
       isCollection = collection.isCollection,
diff --git a/lib/function/trigonometry/acos.js b/lib/function/trigonometry/acos.js
index 457da16ac..608c02460 100644
--- a/lib/function/trigonometry/acos.js
+++ b/lib/function/trigonometry/acos.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       collection = require('../../type/collection'),
 
diff --git a/lib/function/trigonometry/asin.js b/lib/function/trigonometry/asin.js
index 36781d32e..ff28c856b 100644
--- a/lib/function/trigonometry/asin.js
+++ b/lib/function/trigonometry/asin.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       collection = require('../../type/collection'),
 
diff --git a/lib/function/trigonometry/atan.js b/lib/function/trigonometry/atan.js
index 4f35506f6..26ceee5b1 100644
--- a/lib/function/trigonometry/atan.js
+++ b/lib/function/trigonometry/atan.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       collection = require('../../type/collection'),
 
diff --git a/lib/function/trigonometry/atan2.js b/lib/function/trigonometry/atan2.js
index d872d636a..1f62d80c9 100644
--- a/lib/function/trigonometry/atan2.js
+++ b/lib/function/trigonometry/atan2.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       collection = require('../../type/collection'),
 
diff --git a/lib/function/trigonometry/cos.js b/lib/function/trigonometry/cos.js
index ed384ef2c..9c3ea2103 100644
--- a/lib/function/trigonometry/cos.js
+++ b/lib/function/trigonometry/cos.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       Unit = require('../../type/Unit'),
       collection = require('../../type/collection'),
diff --git a/lib/function/trigonometry/cot.js b/lib/function/trigonometry/cot.js
index 087bf8f6e..76313d830 100644
--- a/lib/function/trigonometry/cot.js
+++ b/lib/function/trigonometry/cot.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       Unit = require('../../type/Unit'),
       collection = require('../../type/collection'),
diff --git a/lib/function/trigonometry/csc.js b/lib/function/trigonometry/csc.js
index f70cc1a79..7f6f0ec89 100644
--- a/lib/function/trigonometry/csc.js
+++ b/lib/function/trigonometry/csc.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       Unit = require('../../type/Unit'),
       collection = require('../../type/collection'),
diff --git a/lib/function/trigonometry/sec.js b/lib/function/trigonometry/sec.js
index 4c9f366be..96e020316 100644
--- a/lib/function/trigonometry/sec.js
+++ b/lib/function/trigonometry/sec.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       Unit = require('../../type/Unit'),
       collection = require('../../type/collection'),
diff --git a/lib/function/trigonometry/sin.js b/lib/function/trigonometry/sin.js
index 3f299174c..4252153ea 100644
--- a/lib/function/trigonometry/sin.js
+++ b/lib/function/trigonometry/sin.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       Unit = require('../../type/Unit'),
       collection = require('../../type/collection'),
diff --git a/lib/function/trigonometry/tan.js b/lib/function/trigonometry/tan.js
index 8a9e20c7d..f2cf77c12 100644
--- a/lib/function/trigonometry/tan.js
+++ b/lib/function/trigonometry/tan.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       Unit = require('../../type/Unit'),
       collection = require('../../type/collection'),
diff --git a/lib/function/utils/ifElse.js b/lib/function/utils/ifElse.js
index 8bb7666c7..35ce578e7 100644
--- a/lib/function/utils/ifElse.js
+++ b/lib/function/utils/ifElse.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var util = require('../../util/index'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Matrix = require('../../type/Matrix'),
       Complex = require('../../type/Complex'),
       Unit = require('../../type/Unit'),
diff --git a/lib/function/utils/typeof.js b/lib/function/utils/typeof.js
index 51d990be8..fe1fc7a09 100644
--- a/lib/function/utils/typeof.js
+++ b/lib/function/utils/typeof.js
@@ -1,7 +1,7 @@
 module.exports = function (math) {
   var types = require('../../util/types'),
 
-      BigNumber = require('bignumber.js'),
+      BigNumber = require('../../type/BigNumber'),
       Complex = require('../../type/Complex'),
       Matrix = require('../../type/Matrix'),
       Unit = require('../../type/Unit'),
diff --git a/lib/math.js b/lib/math.js
index 941ed3737..ef9286a60 100644
--- a/lib/math.js
+++ b/lib/math.js
@@ -33,7 +33,10 @@ function mathjs (settings) {
     matrix: 'matrix',
 
     // type of default number output. Choose 'number' (default) or 'bignumber'
-    number: 'number'
+    number: 'number',
+
+    // number of significant digits in bignumbers
+    decimals: 20
   };
 
   /**
@@ -49,7 +52,7 @@ function mathjs (settings) {
    * @return {Object} settings   The currently applied settings
    */
   math.config = function config (settings) {
-    var BigNumber = require('bignumber.js');
+    var BigNumber = require('./type/BigNumber');
 
     if (settings) {
       // merge settings
@@ -57,7 +60,7 @@ function mathjs (settings) {
 
       if (settings.decimals) {
         BigNumber.config({
-          DECIMAL_PLACES: settings.decimals
+          precision: settings.decimals // TODO: rename decimals to precision
         });
       }
 
@@ -87,9 +90,7 @@ function mathjs (settings) {
     }
 
     // return a clone of the settings
-    var current = object.clone(_settings);
-    current.decimals = BigNumber.config().DECIMAL_PLACES;
-    return current;
+    return object.clone(_settings);
   };
 
   // apply provided configuration settings
@@ -107,7 +108,7 @@ function mathjs (settings) {
 
   // types (Matrix, Complex, Unit, ...)
   math.type = {};
-  math.type.BigNumber = require('bignumber.js');
+  math.type.BigNumber = require('./type/BigNumber').constructor(); // create a new Decimal factory for this instance of math.js
   math.type.Complex = require('./type/Complex');
   math.type.Range = require('./type/Range');
   math.type.Index = require('./type/Index');
diff --git a/lib/type/BigNumber.js b/lib/type/BigNumber.js
new file mode 100644
index 000000000..b66d4c71a
--- /dev/null
+++ b/lib/type/BigNumber.js
@@ -0,0 +1 @@
+module.exports = require('decimal.js');
diff --git a/lib/util/number.js b/lib/util/number.js
index df2ed3dd7..a90e0ac33 100644
--- a/lib/util/number.js
+++ b/lib/util/number.js
@@ -1,4 +1,4 @@
-var BigNumber = require('bignumber.js');
+var BigNumber = require('../type/BigNumber');
 
 /**
  * Test whether value is a Number
@@ -166,16 +166,14 @@ exports.format = function format(value, options) {
         throw new Error('options.scientific is deprecated, use options.exponential instead.');
       }
 
-      // adjust BigNumber configuration
+      // create a clone of the bignumber with the desired configuration
       var isBigNumber = value instanceof BigNumber;
       if (isBigNumber) {
-        var oldScientific = BigNumber.config().EXPONENTIAL_AT;
-        BigNumber.config({
-          EXPONENTIAL_AT: [
-            Math.round(Math.log(lower) / Math.LN10),
-            Math.round(Math.log(upper) / Math.LN10)
-          ]
+        var BN = BigNumber.config({
+          toExpNeg: Math.round(Math.log(lower) / Math.LN10),
+          toExpPos: Math.round(Math.log(upper) / Math.LN10)
         });
+        value = new BN(value);
       }
 
       // handle special case zero
@@ -203,10 +201,12 @@ exports.format = function format(value, options) {
         str = exports.toExponential(value, precision);
       }
 
+      /* TODO: cleanup
       // restore BigNumber configuration
       if (isBigNumber) {
         BigNumber.config({EXPONENTIAL_AT: oldScientific});
       }
+      */
 
       // remove trailing zeros after the decimal point
       return str.replace(/((\.\d*?)(0+))($|e)/, function () {
diff --git a/lib/util/string.js b/lib/util/string.js
index 5160da4c4..ca5a6eec0 100644
--- a/lib/util/string.js
+++ b/lib/util/string.js
@@ -1,5 +1,5 @@
 var number = require('./number'),
-    BigNumber = require('bignumber.js');
+    BigNumber = require('../type/BigNumber');
 
 /**
  * Test whether value is a String
diff --git a/package.json b/package.json
index d34f2d3a6..00b80d34c 100644
--- a/package.json
+++ b/package.json
@@ -39,7 +39,7 @@
     "unit"
   ],
   "dependencies": {
-    "bignumber.js": "^1.3.0"
+    "decimal.js": "^1.0.0"
   },
   "devDependencies": {
     "webpack": "latest",
diff --git a/test/expression/node/ConstantNode.test.js b/test/expression/node/ConstantNode.test.js
index f5cb492e0..03c6775f8 100644
--- a/test/expression/node/ConstantNode.test.js
+++ b/test/expression/node/ConstantNode.test.js
@@ -4,7 +4,7 @@ var assert = require('assert'),
     math = require('../../../index')(),
     bigmath = require('../../../index')({number: 'bignumber'}),
     Complex = require('../../../lib/type/Complex'),
-    BigNumber = require('bignumber.js'),
+    BigNumber = require('../../../lib/type/BigNumber'),
     Node = require('../../../lib/expression/node/Node'),
     ConstantNode = require('../../../lib/expression/node/ConstantNode'),
     SymbolNode = require('../../../lib/expression/node/SymbolNode');
diff --git a/test/function/arithmetic/ceil.test.js b/test/function/arithmetic/ceil.test.js
index 85005d00f..a62eef0ee 100644
--- a/test/function/arithmetic/ceil.test.js
+++ b/test/function/arithmetic/ceil.test.js
@@ -30,16 +30,16 @@ describe('ceil', function() {
   });
 
   it('should return the ceil of a big number', function () {
-    approx.deepEqual(ceil(bignumber(0)), bignumber(0));
-    approx.deepEqual(ceil(bignumber(1)), bignumber(1));
-    approx.deepEqual(ceil(bignumber(1.3)), bignumber(2));
-    approx.deepEqual(ceil(bignumber(1.8)), bignumber(2));
-    approx.deepEqual(ceil(bignumber(2)), bignumber(2));
-    approx.deepEqual(ceil(bignumber(-1)), bignumber(-1));
-    approx.deepEqual(ceil(bignumber(-1.3)), bignumber(-1));
-    approx.deepEqual(ceil(bignumber(-1.8)), bignumber(-1));
-    approx.deepEqual(ceil(bignumber(-2)), bignumber(-2));
-    approx.deepEqual(ceil(bignumber(-2.1)), bignumber(-2));
+    assert.deepEqual(ceil(bignumber(0)), bignumber(0));
+    assert.deepEqual(ceil(bignumber(1)), bignumber(1));
+    assert.deepEqual(ceil(bignumber(1.3)), bignumber(2));
+    assert.deepEqual(ceil(bignumber(1.8)), bignumber(2));
+    assert.deepEqual(ceil(bignumber(2)), bignumber(2));
+    assert.deepEqual(ceil(bignumber(-1)), bignumber(-1));
+    assert.deepEqual(ceil(bignumber(-1.3)), bignumber(-1));
+    assert.deepEqual(ceil(bignumber(-1.8)), bignumber(-1));
+    assert.deepEqual(ceil(bignumber(-2)), bignumber(-2));
+    assert.deepEqual(ceil(bignumber(-2.1)), bignumber(-2));
   });
 
   it('should return the ceil of real and imag part of a complex', function() {
diff --git a/test/function/arithmetic/fix.test.js b/test/function/arithmetic/fix.test.js
index ebbd6a437..d4b083c52 100644
--- a/test/function/arithmetic/fix.test.js
+++ b/test/function/arithmetic/fix.test.js
@@ -30,16 +30,16 @@ describe('fix', function() {
   });
 
   it('should round big numbers correctly', function() {
-    approx.deepEqual(fix(bignumber(0)), bignumber(0));
-    approx.deepEqual(fix(bignumber(1)), bignumber(1));
-    approx.deepEqual(fix(bignumber(1.3)), bignumber(1));
-    approx.deepEqual(fix(bignumber(1.8)), bignumber(1));
-    approx.deepEqual(fix(bignumber(2)), bignumber(2));
-    approx.deepEqual(fix(bignumber(-1)), bignumber(-1));
-    approx.deepEqual(fix(bignumber(-1.3)), bignumber(-1));
-    approx.deepEqual(fix(bignumber(-1.8)), bignumber(-1));
-    approx.deepEqual(fix(bignumber(-2)), bignumber(-2));
-    approx.deepEqual(fix(bignumber(-2.1)), bignumber(-2));
+    assert.deepEqual(fix(bignumber(0)), bignumber(0));
+    assert.deepEqual(fix(bignumber(1)), bignumber(1));
+    assert.deepEqual(fix(bignumber(1.3)), bignumber(1));
+    assert.deepEqual(fix(bignumber(1.8)), bignumber(1));
+    assert.deepEqual(fix(bignumber(2)), bignumber(2));
+    assert.deepEqual(fix(bignumber(-1)), bignumber(-1));
+    assert.deepEqual(fix(bignumber(-1.3)), bignumber(-1));
+    assert.deepEqual(fix(bignumber(-1.8)), bignumber(-1));
+    assert.deepEqual(fix(bignumber(-2)), bignumber(-2));
+    assert.deepEqual(fix(bignumber(-2.1)), bignumber(-2));
   });
 
   it('should round complex numbers correctly', function() {
diff --git a/test/function/arithmetic/floor.test.js b/test/function/arithmetic/floor.test.js
index ac4339328..5bbab81d9 100644
--- a/test/function/arithmetic/floor.test.js
+++ b/test/function/arithmetic/floor.test.js
@@ -30,16 +30,16 @@ describe('floor', function() {
   });
 
   it('should floor big numbers correctly', function() {
-    approx.deepEqual(floor(bignumber(0)), bignumber(0));
-    approx.deepEqual(floor(bignumber(1)), bignumber(1));
-    approx.deepEqual(floor(bignumber(1.3)), bignumber(1));
-    approx.deepEqual(floor(bignumber(1.8)), bignumber(1));
-    approx.deepEqual(floor(bignumber(2)), bignumber(2));
-    approx.deepEqual(floor(bignumber(-1)), bignumber(-1));
-    approx.deepEqual(floor(bignumber(-1.3)), bignumber(-2));
-    approx.deepEqual(floor(bignumber(-1.8)), bignumber(-2));
-    approx.deepEqual(floor(bignumber(-2)), bignumber(-2));
-    approx.deepEqual(floor(bignumber(-2.1)), bignumber(-3));
+    assert.deepEqual(floor(bignumber(0)), bignumber(0));
+    assert.deepEqual(floor(bignumber(1)), bignumber(1));
+    assert.deepEqual(floor(bignumber(1.3)), bignumber(1));
+    assert.deepEqual(floor(bignumber(1.8)), bignumber(1));
+    assert.deepEqual(floor(bignumber(2)), bignumber(2));
+    assert.deepEqual(floor(bignumber(-1)), bignumber(-1));
+    assert.deepEqual(floor(bignumber(-1.3)), bignumber(-2));
+    assert.deepEqual(floor(bignumber(-1.8)), bignumber(-2));
+    assert.deepEqual(floor(bignumber(-2)), bignumber(-2));
+    assert.deepEqual(floor(bignumber(-2.1)), bignumber(-3));
   });
 
   it('should floor complex numbers correctly', function() {
diff --git a/test/function/construction/bignumber.test.js b/test/function/construction/bignumber.test.js
index eeb405daa..4c5999e50 100644
--- a/test/function/construction/bignumber.test.js
+++ b/test/function/construction/bignumber.test.js
@@ -1,5 +1,5 @@
 var assert = require('assert'),
-    BigNumber = require('bignumber.js'),
+    BigNumber = require('../../../lib/type/BigNumber'),
     mathjs = require('../../../index'),
     math = mathjs(),
     bignumber = math.bignumber;
diff --git a/test/function/utils/format.test.js b/test/function/utils/format.test.js
index 374187e81..4bdd559c2 100644
--- a/test/function/utils/format.test.js
+++ b/test/function/utils/format.test.js
@@ -1,6 +1,7 @@
 // test format
 var assert = require('assert'),
-    math = require('../../../index')();
+    mathjs = require('../../../index');
+    math = mathjs();
 
 describe('format', function() {
 
@@ -60,9 +61,7 @@ describe('format', function() {
   });
 
   describe('bignumber', function () {
-    before (function () {
-      math.type.BigNumber.config(20); // ensure the precision is 20 digits, the default
-    });
+    var math = mathjs({decimals: 20}); // ensure the precision is 20 digits, the default
 
     it('should format big numbers', function() {
       assert.equal(math.format(math.bignumber(2).dividedBy(7)), '0.28571428571428571429');
diff --git a/test/util/number.test.js b/test/util/number.test.js
index baba3ac2a..0c15aba63 100644
--- a/test/util/number.test.js
+++ b/test/util/number.test.js
@@ -1,7 +1,7 @@
 // test number utils
 var assert = require('assert'),
     approx = require('../../tools/approx'),
-    BigNumber = require('bignumber.js'),
+    BigNumber = require('../../lib/type/BigNumber'),
     number = require('../../lib/util/number');
 
 describe('number', function() {
@@ -75,18 +75,15 @@ describe('number', function() {
   });
 
   it('should format a bignumber using toFixed', function() {
-    var DECIMAL_PLACES = BigNumber.config().DECIMAL_PLACES;
-    BigNumber.config(100);
+    var Big = BigNumber.constructor();
+    Big.config({decimals: 100});
 
-    assert.equal(number.toFixed(new BigNumber(2.34)), '2');
-    assert.equal(number.toFixed(new BigNumber(2.34), 1), '2.3');
-    assert.equal(number.toFixed(new BigNumber(2), 20), '2.00000000000000000000');
-    assert.equal(number.toFixed(new BigNumber(2), 21), '2.000000000000000000000');
-    assert.equal(number.toFixed(new BigNumber(2), 22), '2.0000000000000000000000');
-    assert.equal(number.toFixed(new BigNumber(2), 30), '2.000000000000000000000000000000');
-
-    // restore global bignumber configuration
-    BigNumber.config(DECIMAL_PLACES);
+    assert.equal(number.toFixed(new Big(2.34)), '2');
+    assert.equal(number.toFixed(new Big(2.34), 1), '2.3');
+    assert.equal(number.toFixed(new Big(2), 20), '2.00000000000000000000');
+    assert.equal(number.toFixed(new Big(2), 21), '2.000000000000000000000');
+    assert.equal(number.toFixed(new Big(2), 22), '2.0000000000000000000000');
+    assert.equal(number.toFixed(new Big(2), 30), '2.000000000000000000000000000000');
   });
 
   it('should format a number using toExponential', function() {
@@ -101,22 +98,19 @@ describe('number', function() {
   });
 
   it('should format a bignumber using toExponential', function() {
-    var DECIMAL_PLACES = BigNumber.config().DECIMAL_PLACES;
-    BigNumber.config(100);
+    var Big = BigNumber.constructor();
+    Big.config({decimals: 100});
 
-    assert.equal(number.toExponential(new BigNumber(2.34)), '2.34e+0');
-    assert.equal(number.toExponential(new BigNumber(2.34e+3)), '2.34e+3');
-    assert.equal(number.toExponential(new BigNumber(2.34e-3)), '2.34e-3');
-    assert.equal(number.toExponential(new BigNumber(2.34e+3), 2), '2.3e+3');
-    assert.equal(number.toExponential(new BigNumber(2e+3), 20), '2.0000000000000000000e+3');
-    assert.equal(number.toExponential(new BigNumber(2e+3), 21), '2.00000000000000000000e+3');
-    assert.equal(number.toExponential(new BigNumber(2e+3), 22), '2.000000000000000000000e+3');
-    assert.equal(number.toExponential(new BigNumber(2e+3), 30), '2.00000000000000000000000000000e+3');
-    assert.equal(number.toExponential(new BigNumber('2e+300'), 30), '2.00000000000000000000000000000e+300');
-    assert.equal(number.toExponential(new BigNumber('2e-300'), 30), '2.00000000000000000000000000000e-300');
-
-    // restore global bignumber configuration
-    BigNumber.config(DECIMAL_PLACES);
+    assert.equal(number.toExponential(new Big(2.34)), '2.34e+0');
+    assert.equal(number.toExponential(new Big(2.34e+3)), '2.34e+3');
+    assert.equal(number.toExponential(new Big(2.34e-3)), '2.34e-3');
+    assert.equal(number.toExponential(new Big(2.34e+3), 2), '2.3e+3');
+    assert.equal(number.toExponential(new Big(2e+3), 20), '2.0000000000000000000e+3');
+    assert.equal(number.toExponential(new Big(2e+3), 21), '2.00000000000000000000e+3');
+    assert.equal(number.toExponential(new Big(2e+3), 22), '2.000000000000000000000e+3');
+    assert.equal(number.toExponential(new Big(2e+3), 30), '2.00000000000000000000000000000e+3');
+    assert.equal(number.toExponential(new Big('2e+300'), 30), '2.00000000000000000000000000000e+300');
+    assert.equal(number.toExponential(new Big('2e-300'), 30), '2.00000000000000000000000000000e-300');
   });
 
   it('should convert a number into a bignumber (when possible)', function() {
@@ -334,39 +328,42 @@ describe('number', function() {
     });
 
     describe('bignumber', function () {
+      var B = null;
+
       before (function () {
-        BigNumber.config(20); // ensure the precision is 20 digits, the default
+        B = BigNumber.constructor();
+        B.config({precision: 20}); // ensure the precision is 20 digits, the default
       });
 
       it('should format big numbers', function() {
-        assert.deepEqual(number.format(new BigNumber('2.3')), '2.3');
-        assert.deepEqual(number.format(new BigNumber('0.00000003')), '3e-8');
-        assert.deepEqual(number.format(new BigNumber('12345678')), '1.2345678e+7');
+        assert.deepEqual(number.format(new B('2.3')), '2.3');
+        assert.deepEqual(number.format(new B('0.00000003')), '3e-8');
+        assert.deepEqual(number.format(new B('12345678')), '1.2345678e+7');
       });
 
       it('should format big numbers with given precision', function() {
-        assert.deepEqual(number.format(new BigNumber('1.23456'), 3), '1.23');
-        assert.deepEqual(number.format(new BigNumber('12345678'), 4), '1.235e+7');
+        assert.deepEqual(number.format(new B('1.23456'), 3), '1.23');
+        assert.deepEqual(number.format(new B('12345678'), 4), '1.235e+7');
       });
 
       it('should format big numbers in exponential notation', function() {
         var options = {
           notation: 'exponential'
         };
-        assert.deepEqual(number.format(new BigNumber('1.23456'), options), '1.23456e+0');
-        assert.deepEqual(number.format(new BigNumber('12345678'), options), '1.2345678e+7');
-        assert.deepEqual(number.format(new BigNumber('2.3e+30'), options), '2.3e+30');
-        assert.deepEqual(number.format(new BigNumber('0.23e+30'), options), '2.3e+29');
-        assert.deepEqual(number.format(new BigNumber('2.3e-30'), options), '2.3e-30');
-        assert.deepEqual(number.format(new BigNumber('0.23e-30'), options), '2.3e-31');
+        assert.deepEqual(number.format(new B('1.23456'), options), '1.23456e+0');
+        assert.deepEqual(number.format(new B('12345678'), options), '1.2345678e+7');
+        assert.deepEqual(number.format(new B('2.3e+30'), options), '2.3e+30');
+        assert.deepEqual(number.format(new B('0.23e+30'), options), '2.3e+29');
+        assert.deepEqual(number.format(new B('2.3e-30'), options), '2.3e-30');
+        assert.deepEqual(number.format(new B('0.23e-30'), options), '2.3e-31');
 
         options.precision = 18;
-        assert.deepEqual(number.format(new BigNumber(1).div(3), options), '3.33333333333333333e-1');
+        assert.deepEqual(number.format(new B(1).div(3), options), '3.33333333333333333e-1');
       });
 
-      it.skip('sould format big numbers with custom precision, lower, and upper bound', function() {
-        var oldPrecision = BigNumber.config().DECIMAL_PLACES;
-        BigNumber.config({DECIMAL_PLACES: 100});
+      it('should format big numbers with custom precision, lower, and upper bound', function() {
+        var Big = BigNumber.constructor();
+        Big.config({precision: 100});
 
         var options = {
           notation: 'auto',
@@ -377,16 +374,13 @@ describe('number', function() {
           }
         };
 
-        assert.deepEqual(number.format(new BigNumber(5).div(3), options), '1.6666666666666666666666666666666666666666666666667');
-        assert.deepEqual(number.format(new BigNumber(5e+40).div(3), options), '16666666666666666666666666666666666666666.666666667');
-        assert.deepEqual(number.format(new BigNumber(5e-40).div(3), options),
+        assert.deepEqual(number.format(new Big(5).div(3), options), '1.6666666666666666666666666666666666666666666666667');
+        assert.deepEqual(number.format(new Big(5e+40).div(3), options), '16666666666666666666666666666666666666666.666666667');
+        assert.deepEqual(number.format(new Big(5e-40).div(3), options),
             '0.00000000000000000000000000000000000000016666666666666666666666666666666666666666666666667');
-        assert.deepEqual(number.format(new BigNumber(5e+60).div(3), options), '1.6666666666666666666666666666666666666666666666667e+60');
-        assert.deepEqual(number.format(new BigNumber(5e-60).div(3), options), '1.6666666666666666666666666666666666666666666666667e-60');
-        assert.deepEqual(number.format(new BigNumber(5e-80).div(3), options), '1.6666666666666666666666666666666666666666666666667e-80');
-
-        // restore old precision
-        BigNumber.config({DECIMAL_PLACES: oldPrecision});
+        assert.deepEqual(number.format(new Big(5e+60).div(3), options), '1.6666666666666666666666666666666666666666666666667e+60');
+        assert.deepEqual(number.format(new Big(5e-60).div(3), options), '1.6666666666666666666666666666666666666666666666667e-60');
+        assert.deepEqual(number.format(new Big(5e-80).div(3), options), '1.6666666666666666666666666666666666666666666666667e-80');
       });
 
       it('should format big numbers in fixed notation', function() {