diff --git a/esm/index.js b/esm/index.js
new file mode 100644
index 0000000..3b76d02
--- /dev/null
+++ b/esm/index.js
@@ -0,0 +1,70 @@
+'use strict';
+
+var alphabet = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-_'.split('')
+  , length = 64
+  , map = {}
+  , seed = 0
+  , i = 0
+  , prev;
+
+/**
+ * Return a string representing the specified number.
+ *
+ * @param {Number} num The number to convert.
+ * @returns {String} The string representation of the number.
+ * @api public
+ */
+function encode(num) {
+  var encoded = '';
+
+  do {
+    encoded = alphabet[num % length] + encoded;
+    num = Math.floor(num / length);
+  } while (num > 0);
+
+  return encoded;
+}
+
+/**
+ * Return the integer value specified by the given string.
+ *
+ * @param {String} str The string to convert.
+ * @returns {Number} The integer value represented by the string.
+ * @api public
+ */
+function decode(str) {
+  var decoded = 0;
+
+  for (i = 0; i < str.length; i++) {
+    decoded = decoded * length + map[str.charAt(i)];
+  }
+
+  return decoded;
+}
+
+/**
+ * Yeast: A tiny growing id generator.
+ *
+ * @returns {String} A unique id.
+ * @api public
+ */
+function yeast() {
+  var now = encode(+new Date());
+
+  if (now !== prev) return seed = 0, prev = now;
+  return now +'.'+ encode(seed++);
+}
+
+//
+// Map each character to its index.
+//
+for (; i < length; i++) map[alphabet[i]] = i;
+
+//
+// Expose the `yeast`, `encode` and `decode` functions.
+//
+export {
+  encode,
+  decode,
+  yeast as default
+};
diff --git a/esm/package.json b/esm/package.json
new file mode 100644
index 0000000..3dbc1ca
--- /dev/null
+++ b/esm/package.json
@@ -0,0 +1,3 @@
+{
+  "type": "module"
+}
diff --git a/package.json b/package.json
index e17cb1e..d4d927d 100644
--- a/package.json
+++ b/package.json
@@ -3,6 +3,11 @@
   "version": "0.1.2",
   "description": "Tiny but linear growing unique id generator",
   "main": "index.js",
+  "module": "./esm/index.js",
+  "exports": {
+    "import": "./esm/index.js",
+    "require": "index.js"
+  },
   "scripts": {
     "100%": "istanbul check-coverage --statements 100 --functions 100 --lines 100 --branches 100",
     "test-node": "istanbul cover _mocha --report lcovonly -- test.js",