diff --git a/package.json b/package.json
index bc02fdd6..a92c3267 100644
--- a/package.json
+++ b/package.json
@@ -48,6 +48,8 @@
   },
   "dependencies": {
     "@types/async": "^2.0.41",
-    "async": "^2.5.0"
+    "@types/lodash": "^4.14.73",
+    "async": "^2.5.0",
+    "lodash": "^4.17.4"
   }
 }
diff --git a/src/metadata.ts b/src/metadata.ts
index ffa78996..1936bfa2 100644
--- a/src/metadata.ts
+++ b/src/metadata.ts
@@ -1,35 +1,135 @@
+import { forOwn } from 'lodash';
+
 export type MetadataValue = string | Buffer;
 
 export interface MetadataObject {
-  [propName: string]: Array<MetadataValue>;
+  [key: string]: Array<MetadataValue>;
+}
+
+function cloneMetadataObject(repr: MetadataObject): MetadataObject {
+  const result: MetadataObject = {};
+  forOwn(repr, (value, key) => {
+    // v.slice copies individual buffer values in value.
+    // TODO(kjin): Is this necessary
+    result[key] = value.map(v => {
+      if (v instanceof Buffer) {
+        return v.slice();
+      } else {
+        return v;
+      }
+    });
+  });
+  return result;
+}
+
+function isLegal(legalChars: Array<number>, str: string): boolean {
+  for (let i = 0; i < str.length; i++) {
+    const legalCharsIndex = str.charCodeAt(i) >> 3;
+    if (!(1 << (str.charCodeAt(i) & 7) & legalChars[legalCharsIndex])) {
+      return false;
+    }
+  }
+  return true;
+}
+
+const legalKeyChars = [
+  0x00, 0x00, 0x00, 0x00, 0x00, 0x60, 0xff, 0x03, 0x00, 0x00, 0x00,
+  0x80, 0xfe, 0xff, 0xff, 0x07, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
+];
+const legalNonBinValueChars = [
+  0x00, 0x00, 0x00, 0x00, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+  0xff, 0xff, 0xff, 0xff, 0x7f, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
+];
+
+function isLegalKey(key: string): boolean {
+  return key.length > 0 && isLegal(legalKeyChars, key);
+}
+
+function isLegalNonBinaryValue(value: string): boolean {
+  return isLegal(legalNonBinValueChars, value);
+}
+
+function isBinaryKey(key: string): boolean {
+  return key.endsWith('-bin');
+}
+
+function normalizeKey(key: string): string {
+  return key.toLowerCase();
+}
+
+function validate(key: string, value?: MetadataValue): void {
+  if (!isLegalKey(key)) {
+    throw new Error('Metadata key"' + key + '" contains illegal characters');
+  }
+  if (value != null) {
+    if (isBinaryKey(key)) {
+      if (!(value instanceof Buffer)) {
+        throw new Error('keys that end with \'-bin\' must have Buffer values');
+      }
+    } else {
+      if (value instanceof Buffer) {
+        throw new Error(
+            'keys that don\'t end with \'-bin\' must have String values');
+      }
+      if (!isLegalNonBinaryValue(value)) {
+        throw new Error('Metadata string value "' + value +
+                        '" contains illegal characters');
+      }
+    }
+  }
 }
 
 export class Metadata {
-  static createMetadata(): Metadata {
-    return new Metadata();
+  constructor(private readonly internalRepr: MetadataObject = {}) {}
+
+  set(key: string, value: MetadataValue): void {
+    key = normalizeKey(key);
+    validate(key, value);
+    this.internalRepr[key] = [value];
   }
 
-  set(_key: string, _value: MetadataValue): void {
-    throw new Error('Not implemented');
+  add(key: string, value: MetadataValue): void {
+    key = normalizeKey(key);
+    validate(key, value);
+    if (!this.internalRepr[key]) {
+      this.internalRepr[key] = [value];
+    } else {
+      this.internalRepr[key].push(value);
+    }
   }
 
-  add(_key: string, _value: MetadataValue): void {
-    throw new Error('Not implemented');
+  remove(key: string): void {
+    key = normalizeKey(key);
+    validate(key);
+    if (Object.prototype.hasOwnProperty.call(this.internalRepr, key)) {
+      delete this.internalRepr[key];
+    }
   }
 
-  remove(_key: string): void {
-    throw new Error('Not implemented');
+  get(key: string): Array<MetadataValue> {
+    key = normalizeKey(key);
+    validate(key);
+    if (Object.prototype.hasOwnProperty.call(this.internalRepr, key)) {
+      return this.internalRepr[key];
+    } else {
+      return [];
+    }
   }
 
-  get(_key: string): Array<MetadataValue> {
-    throw new Error('Not implemented');
-  }
-  
-  getMap(): MetadataObject {
-    throw new Error('Not implemented');
+  getMap(): { [key: string]: MetadataValue } {
+    const result: { [key: string]: MetadataValue } = {};
+    forOwn(this.internalRepr, function(values, key) {
+      if(values.length > 0) {
+        const v = values[0];
+        result[key] = v instanceof Buffer ? v.slice() : v;
+      }
+    });
+    return result;
   }
 
   clone(): Metadata {
-    throw new Error('Not implemented');
+    return new Metadata(cloneMetadataObject(this.internalRepr));
   }
 }
diff --git a/test/test-metadata.ts b/test/test-metadata.ts
new file mode 100644
index 00000000..17c89a48
--- /dev/null
+++ b/test/test-metadata.ts
@@ -0,0 +1,182 @@
+import * as assert from 'assert';
+import { Metadata } from '../src/metadata';
+
+describe('Metadata', () => {
+  let metadata: Metadata;
+
+  beforeEach(() => {
+    metadata = new Metadata();
+  });
+
+  describe('set', () => {
+    it('Only accepts string values for non "-bin" keys', () => {
+      assert.throws(() => {
+        metadata.set('key', new Buffer('value'));
+      });
+      assert.doesNotThrow(() => {
+        metadata.set('key', 'value');
+      });
+    });
+
+    it('Only accepts Buffer values for "-bin" keys', () => {
+      assert.throws(() => {
+        metadata.set('key-bin', 'value');
+      });
+      assert.doesNotThrow(() => {
+        metadata.set('key-bin', new Buffer('value'));
+      });
+    });
+
+    it('Rejects invalid keys', () => {
+      assert.throws(() => {
+        metadata.set('key$', 'value');
+      });
+      assert.throws(() => {
+        metadata.set('', 'value');
+      });
+    });
+
+    it('Rejects values with non-ASCII characters', () => {
+      assert.throws(() => {
+        metadata.set('key', 'résumé');
+      });
+    });
+
+    it('Saves values that can be retrieved', () => {
+      metadata.set('key', 'value');
+      assert.deepEqual(metadata.get('key'), ['value']);
+    });
+
+    it('Overwrites previous values', () => {
+      metadata.set('key', 'value1');
+      metadata.set('key', 'value2');
+      assert.deepEqual(metadata.get('key'), ['value2']);
+    });
+
+    it('Normalizes keys', () => {
+      metadata.set('Key', 'value1');
+      assert.deepEqual(metadata.get('key'), ['value1']);
+      metadata.set('KEY', 'value2');
+      assert.deepEqual(metadata.get('key'), ['value2']);
+    });
+  });
+
+  describe('add', () => {
+    it('Only accepts string values for non "-bin" keys', () => {
+      assert.throws(() => {
+        metadata.add('key', new Buffer('value'));
+      });
+      assert.doesNotThrow(() => {
+        metadata.add('key', 'value');
+      });
+    });
+
+    it('Only accepts Buffer values for "-bin" keys', () => {
+      assert.throws(() => {
+        metadata.add('key-bin', 'value');
+      });
+      assert.doesNotThrow(() => {
+        metadata.add('key-bin', new Buffer('value'));
+      });
+    });
+
+    it('Rejects invalid keys', () => {
+      assert.throws(() => {
+        metadata.add('key$', 'value');
+      });
+      assert.throws(() => {
+        metadata.add('', 'value');
+      });
+    });
+
+    it('Saves values that can be retrieved', () => {
+      metadata.add('key', 'value');
+      assert.deepEqual(metadata.get('key'), ['value']);
+    });
+
+    it('Combines with previous values', () => {
+      metadata.add('key', 'value1');
+      metadata.add('key', 'value2');
+      assert.deepEqual(metadata.get('key'), ['value1', 'value2']);
+    });
+
+    it('Normalizes keys', () => {
+      metadata.add('Key', 'value1');
+      assert.deepEqual(metadata.get('key'), ['value1']);
+      metadata.add('KEY', 'value2');
+      assert.deepEqual(metadata.get('key'), ['value1', 'value2']);
+    });
+  });
+
+  describe('remove', () => {
+    it('clears values from a key', () => {
+      metadata.add('key', 'value');
+      metadata.remove('key');
+      assert.deepEqual(metadata.get('key'), []);
+    });
+
+    it('Normalizes keys', () => {
+      metadata.add('key', 'value');
+      metadata.remove('KEY');
+      assert.deepEqual(metadata.get('key'), []);
+    });
+  });
+
+  describe('get', () => {
+    beforeEach(() => {
+      metadata.add('key', 'value1');
+      metadata.add('key', 'value2');
+      metadata.add('key-bin', new Buffer('value'));
+    });
+
+    it('gets all values associated with a key', () => {
+      assert.deepEqual(metadata.get('key'), ['value1', 'value2']);
+    });
+
+    it('Normalizes keys', () => {
+      assert.deepEqual(metadata.get('KEY'), ['value1', 'value2']);
+    });
+
+    it('returns an empty list for non-existent keys', () => {
+      assert.deepEqual(metadata.get('non-existent-key'), []);
+    });
+
+    it('returns Buffers for "-bin" keys', () => {
+      assert.ok(metadata.get('key-bin')[0] instanceof Buffer);
+    });
+  });
+
+  describe('getMap', () => {
+    it('gets a map of keys to values', () => {
+      metadata.add('key1', 'value1');
+      metadata.add('Key2', 'value2');
+      metadata.add('KEY3', 'value3');
+      assert.deepEqual(metadata.getMap(),
+                       {key1: 'value1',
+                        key2: 'value2',
+                        key3: 'value3'});
+    });
+  });
+
+  describe('clone', () => {
+    it('retains values from the original', () => {
+      metadata.add('key', 'value');
+      const copy = metadata.clone();
+      assert.deepEqual(copy.get('key'), ['value']);
+    });
+
+    it('Does not see newly added values', () => {
+      metadata.add('key', 'value1');
+      const copy = metadata.clone();
+      metadata.add('key', 'value2');
+      assert.deepEqual(copy.get('key'), ['value1']);
+    });
+
+    it('Does not add new values to the original', () => {
+      metadata.add('key', 'value1');
+      const copy = metadata.clone();
+      copy.add('key', 'value2');
+      assert.deepEqual(metadata.get('key'), ['value1']);
+    });
+  });
+});
\ No newline at end of file