diff --git a/.gitignore b/.gitignore
index ca77e406f..6167575ed 100644
--- a/.gitignore
+++ b/.gitignore
@@ -4,3 +4,6 @@
 index.html
 package-lock.json
 yarn-error.log
+
+# Perf related files
+isolate*.log
\ No newline at end of file
diff --git a/perf/.gitignore b/perf/.gitignore
new file mode 100644
index 000000000..bc7a91cc4
--- /dev/null
+++ b/perf/.gitignore
@@ -0,0 +1,2 @@
+output*.css
+v8.json
\ No newline at end of file
diff --git a/perf/fixture.css b/perf/fixture.css
new file mode 100644
index 000000000..8de93d6fb
--- /dev/null
+++ b/perf/fixture.css
@@ -0,0 +1,61 @@
+@tailwind base;
+
+@tailwind components;
+
+@tailwind utilities;
+
+
+.btn-1-xl {
+  @apply sm:space-x-0;
+  @apply xl:space-x-0;
+  @apply sm:space-x-1;
+  @apply xl:space-x-1;
+  @apply sm:space-y-0;
+  @apply xl:space-y-0;
+  @apply sm:space-y-1;
+  @apply xl:space-y-1;
+}
+.btn-2-xl {
+  @apply sm:space-x-0;
+  @apply xl:space-x-0;
+  @apply sm:space-x-1;
+  @apply xl:space-x-1;
+  @apply sm:space-y-0;
+  @apply xl:space-y-0;
+  @apply sm:space-y-1;
+  @apply xl:space-y-1;
+  @apply btn-1-xl;
+}
+.btn-3-xl {
+  @apply sm:space-x-0;
+  @apply xl:space-x-0;
+  @apply sm:space-x-1;
+  @apply xl:space-x-1;
+  @apply sm:space-y-0;
+  @apply xl:space-y-0;
+  @apply sm:space-y-1;
+  @apply xl:space-y-1;
+  @apply btn-2-xl;
+}
+.btn-4-xl {
+  @apply sm:space-x-0;
+  @apply xl:space-x-0;
+  @apply sm:space-x-1;
+  @apply xl:space-x-1;
+  @apply sm:space-y-0;
+  @apply xl:space-y-0;
+  @apply sm:space-y-1;
+  @apply xl:space-y-1;
+  @apply btn-3-xl;
+}
+.btn-5-xl {
+  @apply sm:space-x-0;
+  @apply xl:space-x-0;
+  @apply sm:space-x-1;
+  @apply xl:space-x-1;
+  @apply sm:space-y-0;
+  @apply xl:space-y-0;
+  @apply sm:space-y-1;
+  @apply xl:space-y-1;
+  @apply btn-4-xl;
+}
diff --git a/perf/script.sh b/perf/script.sh
new file mode 100755
index 000000000..cad09f2f3
--- /dev/null
+++ b/perf/script.sh
@@ -0,0 +1,15 @@
+# Cleanup existing perf stuff
+rm isolate-*.log
+
+# Ensure we use the latest build version
+npm run babelify
+
+# Run Tailwind on the big fixture file & profile it
+node --prof lib/cli.js build ./perf/fixture.css -c ./perf/tailwind.config.js -o ./perf/output.css
+
+# Generate flame graph
+node --prof-process --preprocess -j isolate*.log > ./perf/v8.json
+
+# Now visit: https://mapbox.github.io/flamebearer/
+# And drag that v8.json file in there!
+# You can put "./lib" in the search box which will highlight all our code in green.
\ No newline at end of file
diff --git a/perf/tailwind.config.js b/perf/tailwind.config.js
new file mode 100644
index 000000000..7fb2125aa
--- /dev/null
+++ b/perf/tailwind.config.js
@@ -0,0 +1,28 @@
+module.exports = {
+  future: 'all',
+  experimental: 'all',
+  purge: [],
+  theme: {
+    extend: {},
+  },
+  variants: [
+    'responsive',
+    'motion-safe',
+    'motion-reduce',
+    'group-hover',
+    'group-focus',
+    'hover',
+    'focus-within',
+    'focus-visible',
+    'focus',
+    'active',
+    'visited',
+    'disabled',
+    'checked',
+    'first',
+    'last',
+    'odd',
+    'even',
+  ],
+  plugins: [],
+}
diff --git a/src/flagged/applyComplexClasses.js b/src/flagged/applyComplexClasses.js
index 9b1d7e8f7..fe1ba1217 100644
--- a/src/flagged/applyComplexClasses.js
+++ b/src/flagged/applyComplexClasses.js
@@ -8,6 +8,7 @@ import substituteResponsiveAtRules from '../lib/substituteResponsiveAtRules'
 import convertLayerAtRulesToControlComments from '../lib/convertLayerAtRulesToControlComments'
 import substituteScreenAtRules from '../lib/substituteScreenAtRules'
 import prefixSelector from '../util/prefixSelector'
+import { useMemo } from '../util/useMemo'
 
 function hasAtRule(css, atRule) {
   let foundAtRule = false
@@ -20,26 +21,39 @@ function hasAtRule(css, atRule) {
   return foundAtRule
 }
 
-function generateRulesFromApply({ rule, utilityName: className, classPosition }, replaceWith) {
-  const processedSelectors = rule.selectors.map(selector => {
-    const processor = selectorParser(selectors => {
-      let i = 0
-      selectors.walkClasses(c => {
-        if (c.value === className && classPosition === i) {
-          c.replaceWith(selectorParser.attribute({ attribute: '__TAILWIND-APPLY-PLACEHOLDER__' }))
-        }
-        i++
-      })
-    })
+function cloneWithoutChildren(node) {
+  if (node.type === 'atrule') {
+    return postcss.atRule({ name: node.name, params: node.params })
+  }
 
+  if (node.type === 'rule') {
+    return postcss.rule({ name: node.name, selectors: node.selectors })
+  }
+
+  const clone = node.clone()
+  clone.removeAll()
+  return clone
+}
+
+const tailwindApplyPlaceholder = selectorParser.attribute({
+  attribute: '__TAILWIND-APPLY-PLACEHOLDER__',
+})
+
+function generateRulesFromApply({ rule, utilityName: className, classPosition }, replaceWith) {
+  const parser = selectorParser(selectors => {
+    let i = 0
+    selectors.walkClasses(c => {
+      if (classPosition === i++ && c.value === className) {
+        c.replaceWith(tailwindApplyPlaceholder)
+      }
+    })
+  })
+
+  const processedSelectors = rule.selectors.map(selector => {
     // You could argue we should make this replacement at the AST level, but if we believe
     // the placeholder string is safe from collisions then it is safe to do this is a simple
     // string replacement, and much, much faster.
-    const processedSelector = processor
-      .processSync(selector)
-      .replace('[__TAILWIND-APPLY-PLACEHOLDER__]', replaceWith)
-
-    return processedSelector
+    return parser.processSync(selector).replace('[__TAILWIND-APPLY-PLACEHOLDER__]', replaceWith)
   })
 
   const cloned = rule.clone()
@@ -47,8 +61,8 @@ function generateRulesFromApply({ rule, utilityName: className, classPosition },
   let parent = rule.parent
 
   while (parent && parent.type !== 'root') {
-    const parentClone = parent.clone()
-    parentClone.removeAll()
+    const parentClone = cloneWithoutChildren(parent)
+
     parentClone.append(current)
     current.parent = parentClone
     current = parentClone
@@ -59,19 +73,21 @@ function generateRulesFromApply({ rule, utilityName: className, classPosition },
   return current
 }
 
-function extractUtilityNames(selector) {
-  const processor = selectorParser(selectors => {
-    let classes = []
+const extractUtilityNamesParser = selectorParser(selectors => {
+  let classes = []
+  selectors.walkClasses(c => classes.push(c.value))
+  return classes
+})
 
-    selectors.walkClasses(c => {
-      classes.push(c)
-    })
+const extractUtilityNames = useMemo(
+  selector => extractUtilityNamesParser.transformSync(selector),
+  selector => selector
+)
 
-    return classes.map(c => c.value)
-  })
-
-  return processor.transformSync(selector)
-}
+const cloneRuleWithParent = useMemo(
+  rule => rule.clone({ parent: rule.parent }),
+  rule => rule
+)
 
 function buildUtilityMap(css) {
   let index = 0
@@ -89,8 +105,9 @@ function buildUtilityMap(css) {
         index,
         utilityName,
         classPosition: i,
-        rule: rule.clone({ parent: rule.parent }),
-        containsApply: hasAtRule(rule, 'apply'),
+        get rule() {
+          return cloneRuleWithParent(rule)
+        },
       })
       index++
     })
@@ -136,15 +153,11 @@ function mergeAdjacentRules(initialRule, rulesToInsert) {
 
 function makeExtractUtilityRules(css, config) {
   const utilityMap = buildUtilityMap(css)
-  const orderUtilityMap = _.fromPairs(
-    _.flatMap(_.toPairs(utilityMap), ([_utilityName, utilities]) => {
-      return utilities.map(utility => {
-        return [utility.index, utility]
-      })
-    })
-  )
-  return function(utilityNames, rule) {
-    return _.flatMap(utilityNames, utilityName => {
+
+  return function extractUtilityRules(utilityNames, rule) {
+    const combined = []
+
+    utilityNames.forEach(utilityName => {
       if (utilityMap[utilityName] === undefined) {
         // Look for prefixed utility in case the user has goofed
         const prefixedUtility = prefixSelector(config.prefix, `.${utilityName}`).slice(1)
@@ -160,17 +173,18 @@ function makeExtractUtilityRules(css, config) {
           { word: utilityName }
         )
       }
-      return utilityMap[utilityName].map(({ index }) => index)
+
+      combined.push(...utilityMap[utilityName])
     })
-      .sort((a, b) => a - b)
-      .map(i => orderUtilityMap[i])
+
+    return combined.sort((a, b) => a.index - b.index)
   }
 }
 
 function processApplyAtRules(css, lookupTree, config) {
   const extractUtilityRules = makeExtractUtilityRules(lookupTree, config)
 
-  while (hasAtRule(css, 'apply')) {
+  do {
     css.walkRules(rule => {
       const applyRules = []
 
@@ -229,13 +243,29 @@ function processApplyAtRules(css, lookupTree, config) {
         rule.remove()
       }
     })
-  }
+
+    // We already know that we have at least 1 @apply rule. Otherwise this
+    // function would not have been called. Therefore we can execute this code
+    // at least once. This also means that in the best case scenario we only
+    // call this 2 times, instead of 3 times.
+    // 1st time -> before we call this function
+    // 2nd time -> when we check if we have to do this loop again (because do {} while (check))
+    // .. instead of
+    // 1st time -> before we call this function
+    // 2nd time -> when we check the first time (because while (check) do {})
+    // 3rd time -> when we re-check to see if we should do this loop again
+  } while (hasAtRule(css, 'apply'))
 
   return css
 }
 
 export default function applyComplexClasses(config, getProcessedPlugins) {
   return function(css) {
+    // We can stop already when we don't have any @apply rules. Vue users: you're welcome!
+    if (!hasAtRule(css, 'apply')) {
+      return css
+    }
+
     // Tree already contains @tailwind rules, don't prepend default Tailwind tree
     if (hasAtRule(css, 'tailwind')) {
       return processApplyAtRules(css, css, config)
@@ -261,7 +291,7 @@ export default function applyComplexClasses(config, getProcessedPlugins) {
       )
       .then(result => {
         // Prepend Tailwind's generated classes to the tree so they are available for `@apply`
-        const lookupTree = _.tap(css.clone(), tree => tree.prepend(result.root))
+        const lookupTree = _.tap(result.root, tree => tree.append(css.clone()))
         return processApplyAtRules(css, lookupTree, config)
       })
   }
diff --git a/src/lib/substituteVariantsAtRules.js b/src/lib/substituteVariantsAtRules.js
index 578d57343..1cf189559 100644
--- a/src/lib/substituteVariantsAtRules.js
+++ b/src/lib/substituteVariantsAtRules.js
@@ -6,14 +6,14 @@ import prefixSelector from '../util/prefixSelector'
 
 function generatePseudoClassVariant(pseudoClass, selectorPrefix = pseudoClass) {
   return generateVariantFunction(({ modifySelectors, separator }) => {
-    return modifySelectors(({ selector }) => {
-      return selectorParser(selectors => {
-        selectors.walkClasses(sel => {
-          sel.value = `${selectorPrefix}${separator}${sel.value}`
-          sel.parent.insertAfter(sel, selectorParser.pseudo({ value: `:${pseudoClass}` }))
-        })
-      }).processSync(selector)
+    const parser = selectorParser(selectors => {
+      selectors.walkClasses(sel => {
+        sel.value = `${selectorPrefix}${separator}${sel.value}`
+        sel.parent.insertAfter(sel, selectorParser.pseudo({ value: `:${pseudoClass}` }))
+      })
     })
+
+    return modifySelectors(({ selector }) => parser.processSync(selector))
   })
 }
 
@@ -24,13 +24,12 @@ function ensureIncludesDefault(variants) {
 const defaultVariantGenerators = config => ({
   default: generateVariantFunction(() => {}),
   'motion-safe': generateVariantFunction(({ container, separator, modifySelectors }) => {
-    const modified = modifySelectors(({ selector }) => {
-      return selectorParser(selectors => {
-        selectors.walkClasses(sel => {
-          sel.value = `motion-safe${separator}${sel.value}`
-        })
-      }).processSync(selector)
+    const parser = selectorParser(selectors => {
+      selectors.walkClasses(sel => {
+        sel.value = `motion-safe${separator}${sel.value}`
+      })
     })
+    const modified = modifySelectors(({ selector }) => parser.processSync(selector))
     const mediaQuery = postcss.atRule({
       name: 'media',
       params: '(prefers-reduced-motion: no-preference)',
@@ -39,42 +38,42 @@ const defaultVariantGenerators = config => ({
     container.append(mediaQuery)
   }),
   'motion-reduce': generateVariantFunction(({ container, separator, modifySelectors }) => {
-    const modified = modifySelectors(({ selector }) => {
-      return selectorParser(selectors => {
-        selectors.walkClasses(sel => {
-          sel.value = `motion-reduce${separator}${sel.value}`
-        })
-      }).processSync(selector)
+    const parser = selectorParser(selectors => {
+      selectors.walkClasses(sel => {
+        sel.value = `motion-reduce${separator}${sel.value}`
+      })
+    })
+    const modified = modifySelectors(({ selector }) => parser.processSync(selector))
+    const mediaQuery = postcss.atRule({
+      name: 'media',
+      params: '(prefers-reduced-motion: reduce)',
     })
-    const mediaQuery = postcss.atRule({ name: 'media', params: '(prefers-reduced-motion: reduce)' })
     mediaQuery.append(modified)
     container.append(mediaQuery)
   }),
   'group-hover': generateVariantFunction(({ modifySelectors, separator }) => {
-    return modifySelectors(({ selector }) => {
-      return selectorParser(selectors => {
-        selectors.walkClasses(sel => {
-          sel.value = `group-hover${separator}${sel.value}`
-          sel.parent.insertBefore(
-            sel,
-            selectorParser().astSync(prefixSelector(config.prefix, '.group:hover '))
-          )
-        })
-      }).processSync(selector)
+    const parser = selectorParser(selectors => {
+      selectors.walkClasses(sel => {
+        sel.value = `group-hover${separator}${sel.value}`
+        sel.parent.insertBefore(
+          sel,
+          selectorParser().astSync(prefixSelector(config.prefix, '.group:hover '))
+        )
+      })
     })
+    return modifySelectors(({ selector }) => parser.processSync(selector))
   }),
   'group-focus': generateVariantFunction(({ modifySelectors, separator }) => {
-    return modifySelectors(({ selector }) => {
-      return selectorParser(selectors => {
-        selectors.walkClasses(sel => {
-          sel.value = `group-focus${separator}${sel.value}`
-          sel.parent.insertBefore(
-            sel,
-            selectorParser().astSync(prefixSelector(config.prefix, '.group:focus '))
-          )
-        })
-      }).processSync(selector)
+    const parser = selectorParser(selectors => {
+      selectors.walkClasses(sel => {
+        sel.value = `group-focus${separator}${sel.value}`
+        sel.parent.insertBefore(
+          sel,
+          selectorParser().astSync(prefixSelector(config.prefix, '.group:focus '))
+        )
+      })
     })
+    return modifySelectors(({ selector }) => parser.processSync(selector))
   }),
   hover: generatePseudoClassVariant('hover'),
   'focus-within': generatePseudoClassVariant('focus-within'),
diff --git a/src/util/buildSelectorVariant.js b/src/util/buildSelectorVariant.js
index a7c938f45..77c0b680d 100644
--- a/src/util/buildSelectorVariant.js
+++ b/src/util/buildSelectorVariant.js
@@ -1,15 +1,21 @@
 import parser from 'postcss-selector-parser'
 import tap from 'lodash/tap'
+import { useMemo } from './useMemo'
 
-export default function buildSelectorVariant(selector, variantName, separator, onError = () => {}) {
-  return parser(selectors => {
-    tap(selectors.first.filter(({ type }) => type === 'class').pop(), classSelector => {
-      if (classSelector === undefined) {
-        onError('Variant cannot be generated because selector contains no classes.')
-        return
-      }
+const buildSelectorVariant = useMemo(
+  (selector, variantName, separator, onError = () => {}) => {
+    return parser(selectors => {
+      tap(selectors.first.filter(({ type }) => type === 'class').pop(), classSelector => {
+        if (classSelector === undefined) {
+          onError('Variant cannot be generated because selector contains no classes.')
+          return
+        }
 
-      classSelector.value = `${variantName}${separator}${classSelector.value}`
-    })
-  }).processSync(selector)
-}
+        classSelector.value = `${variantName}${separator}${classSelector.value}`
+      })
+    }).processSync(selector)
+  },
+  (selector, variantName, separator) => [selector, variantName, separator].join('||')
+)
+
+export default buildSelectorVariant
diff --git a/src/util/generateVariantFunction.js b/src/util/generateVariantFunction.js
index 67b8fe230..8de4e4867 100644
--- a/src/util/generateVariantFunction.js
+++ b/src/util/generateVariantFunction.js
@@ -1,6 +1,16 @@
 import _ from 'lodash'
 import postcss from 'postcss'
 import selectorParser from 'postcss-selector-parser'
+import { useMemo } from './useMemo'
+
+const classNameParser = selectorParser(selectors => {
+  return selectors.first.filter(({ type }) => type === 'class').pop().value
+})
+
+const getClassNameFromSelector = useMemo(
+  selector => classNameParser.transformSync(selector),
+  selector => selector
+)
 
 export default function generateVariantFunction(generator) {
   return (container, config) => {
@@ -18,12 +28,10 @@ export default function generateVariantFunction(generator) {
               }
 
               rule.selectors = rule.selectors.map(selector => {
-                const className = selectorParser(selectors => {
-                  return selectors.first.filter(({ type }) => type === 'class').pop().value
-                }).transformSync(selector)
-
                 return modifierFunction({
-                  className,
+                  get className() {
+                    return getClassNameFromSelector(selector)
+                  },
                   selector,
                 })
               })
diff --git a/src/util/useMemo.js b/src/util/useMemo.js
new file mode 100644
index 000000000..a70c397f0
--- /dev/null
+++ b/src/util/useMemo.js
@@ -0,0 +1,16 @@
+export function useMemo(cb, keyResolver) {
+  const cache = new Map()
+
+  return (...args) => {
+    const key = keyResolver(...args)
+
+    if (cache.has(key)) {
+      return cache.get(key)
+    }
+
+    const result = cb(...args)
+    cache.set(key, result)
+
+    return result
+  }
+}