diff --git a/packages/custom-properties/.npmignore b/packages/custom-properties/.npmignore
new file mode 100644
index 000000000..37ccaba94
--- /dev/null
+++ b/packages/custom-properties/.npmignore
@@ -0,0 +1,3 @@
+babel.config.js
+test
+coverage
diff --git a/packages/custom-properties/README.md b/packages/custom-properties/README.md
new file mode 100644
index 000000000..df4b79535
--- /dev/null
+++ b/packages/custom-properties/README.md
@@ -0,0 +1,39 @@
+# @theme-ui/custom-properties
+
+Generate CSS custom properties for use with Theme UI.
+
+
+## Installation
+
+```
+yarn add @theme-ui/custom-properties
+```
+
+
+## Usage
+
+Transform your Theme UI compliant theme config with the library:
+
+```js
+const toCustomProperties = require('@theme-ui/custom-properties')
+const theme = require('../theme');
+
+module.exports = () => {
+  const customProperties = toCustomProperties(theme, '🍭');
+
+  return customProperties;
+}
+```
+
+
+## Parameters
+
+The @theme-ui/custom-properties function takes two parameters:
+
+```js
+toCustomProperties( $theme, $prefix );
+```
+
+1. theme - The theme ui specification object
+1. prefix - An optional prefix for the css custom property _optional_
+
diff --git a/packages/custom-properties/babel.config.js b/packages/custom-properties/babel.config.js
new file mode 100644
index 000000000..46bf5309f
--- /dev/null
+++ b/packages/custom-properties/babel.config.js
@@ -0,0 +1 @@
+module.exports = require('../../babel.config')
diff --git a/packages/custom-properties/package.json b/packages/custom-properties/package.json
new file mode 100644
index 000000000..00359e23a
--- /dev/null
+++ b/packages/custom-properties/package.json
@@ -0,0 +1,20 @@
+{
+  "name": "@theme-ui/custom-properties",
+  "description": "Generate CSS custom properties for use with Theme UI",
+  "version": "0.0.0",
+  "main": "dist/index.js",
+  "module": "dist/index.esm.js",
+  "author": "Alex Page <alex@alexpage.com.au>",
+  "license": "MIT",
+  "scripts": {
+    "prepare": "microbundle --no-compress",
+    "watch": "microbundle watch --no-compress"
+  },
+  "devDependencies": {},
+  "publishConfig": {
+    "access": "public"
+  },
+  "dependencies": {
+    "pluralize": "^8.0.0"
+  }
+}
diff --git a/packages/custom-properties/src/index.js b/packages/custom-properties/src/index.js
new file mode 100644
index 000000000..3f47710e2
--- /dev/null
+++ b/packages/custom-properties/src/index.js
@@ -0,0 +1,33 @@
+import pluralize from 'pluralize'
+
+export default (theme, prefix) => {
+  const customProperties = {}
+
+  const generateProperties = (object, previousKey) => {
+    Object.entries(object).forEach(([key, value]) => {
+      let formattedKey = pluralize(key, 1)
+
+      if (prefix && !previousKey) {
+        formattedKey = `${prefix}-${formattedKey}`
+      }
+
+      const newKey = previousKey
+        ? previousKey + '-' + formattedKey
+        : formattedKey
+
+      if (Array.isArray(value)) {
+        value.forEach((item, i) => {
+          customProperties[`--${newKey}-${i}`] = item
+        })
+      } else if (Object(value) === value) {
+        generateProperties(value, newKey)
+      } else {
+        customProperties[`--${newKey}`] = value
+      }
+    })
+  }
+
+  generateProperties(theme)
+
+  return customProperties
+}
diff --git a/packages/custom-properties/test/__snapshots__/test.js.snap b/packages/custom-properties/test/__snapshots__/test.js.snap
new file mode 100644
index 000000000..0c924f485
--- /dev/null
+++ b/packages/custom-properties/test/__snapshots__/test.js.snap
@@ -0,0 +1,63 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`transforms a theme config to CSS custom properties 1`] = `
+Object {
+  "--color-accent": "#609",
+  "--color-background": "#fff",
+  "--color-dark-background-surface": "#fff",
+  "--color-dark-foreground-text": "#000",
+  "--color-muted": "#f6f6f6",
+  "--color-primary": "#07c",
+  "--color-secondary": "#05a",
+  "--color-text": "#000",
+  "--font-body": "system-ui, sans-serif",
+  "--font-heading": "system-ui, sans-serif",
+  "--font-monospace": "Menlo, monospace",
+  "--fontWeight-body": 400,
+  "--fontWeight-bold": 700,
+  "--fontWeight-heading": 700,
+  "--lineHeight-0": 1.5,
+  "--lineHeight-1": 1.125,
+  "--size-0": "10em",
+  "--size-1": "20em",
+  "--size-2": "30em",
+  "--size-3": "40em",
+  "--space-0": 0,
+  "--space-1": 2,
+  "--space-2": 3,
+  "--space-3": 4,
+  "--space-4": 5,
+  "--space-5": 6,
+}
+`;
+
+exports[`transforms a theme config to CSS custom properties with prefix 1`] = `
+Object {
+  "--🍭-color-accent": "#609",
+  "--🍭-color-background": "#fff",
+  "--🍭-color-dark-background-surface": "#fff",
+  "--🍭-color-dark-foreground-text": "#000",
+  "--🍭-color-muted": "#f6f6f6",
+  "--🍭-color-primary": "#07c",
+  "--🍭-color-secondary": "#05a",
+  "--🍭-color-text": "#000",
+  "--🍭-font-body": "system-ui, sans-serif",
+  "--🍭-font-heading": "system-ui, sans-serif",
+  "--🍭-font-monospace": "Menlo, monospace",
+  "--🍭-fontWeight-body": 400,
+  "--🍭-fontWeight-bold": 700,
+  "--🍭-fontWeight-heading": 700,
+  "--🍭-lineHeight-0": 1.5,
+  "--🍭-lineHeight-1": 1.125,
+  "--🍭-size-0": "10em",
+  "--🍭-size-1": "20em",
+  "--🍭-size-2": "30em",
+  "--🍭-size-3": "40em",
+  "--🍭-space-0": 0,
+  "--🍭-space-1": 2,
+  "--🍭-space-2": 3,
+  "--🍭-space-3": 4,
+  "--🍭-space-4": 5,
+  "--🍭-space-5": 6,
+}
+`;
diff --git a/packages/custom-properties/test/test.js b/packages/custom-properties/test/test.js
new file mode 100644
index 000000000..aa90c46ec
--- /dev/null
+++ b/packages/custom-properties/test/test.js
@@ -0,0 +1,45 @@
+import toCustomProperties from '../src'
+
+const theme = {
+  colors: {
+    text: '#000',
+    background: '#fff',
+    primary: '#07c',
+    secondary: '#05a',
+    accent: '#609',
+    muted: '#f6f6f6',
+    dark: {
+      foreground: {
+        text: '#000',
+      },
+      background: {
+        surface: '#fff',
+      },
+    },
+  },
+  fonts: {
+    body: 'system-ui, sans-serif',
+    heading: 'system-ui, sans-serif',
+    monospace: 'Menlo, monospace',
+  },
+  fontWeights: {
+    body: 400,
+    heading: 700,
+    bold: 700,
+  },
+  lineHeights: [1.5, 1.125],
+  space: [0, 2, 3, 4, 5, 6],
+  size: ['10em', '20em', '30em', '40em'],
+}
+
+it('transforms a theme config to CSS custom properties', () => {
+  const result = toCustomProperties(theme)
+
+  expect(result).toMatchSnapshot()
+})
+
+it('transforms a theme config to CSS custom properties with prefix', () => {
+  const result = toCustomProperties(theme, '🍭')
+
+  expect(result).toMatchSnapshot()
+})
diff --git a/yarn.lock b/yarn.lock
index aad722802..62267efbc 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -15988,6 +15988,11 @@ please-upgrade-node@^3.1.1:
   dependencies:
     semver-compare "^1.0.0"
 
+pluralize@^8.0.0:
+  version "8.0.0"
+  resolved "https://registry.yarnpkg.com/pluralize/-/pluralize-8.0.0.tgz#1a6fa16a38d12a1901e0320fa017051c539ce3b1"
+  integrity sha512-Nc3IT5yHzflTfbjgqWcCPpo7DaKy4FnpB0l/zCAW0Tc7jxAiuqSxHasntB3D7887LSrA93kDJ9IXovxJYxyLCA==
+
 pn@^1.1.0:
   version "1.1.0"
   resolved "https://registry.yarnpkg.com/pn/-/pn-1.1.0.tgz#e2f4cef0e219f463c179ab37463e4e1ecdccbafb"