diff --git a/README.md b/README.md
index 66c168c..39aab03 100644
--- a/README.md
+++ b/README.md
@@ -30,6 +30,12 @@ ns1.register({
 Hyperschema.toDisk(schema)
 ```
 
+If you want to generate as ESM, simply use `import` instead of `require` above or set the option explictly in `toDisk` like so
+
+```js
+Hyperschema.toDisk(schema, { esm: true })
+```
+
 `index.js` will contain generated `compact-encoding` definitions. You can then load/use them as follows:
 ```js
 const c = require('compact-encoding')
diff --git a/index.js b/builder.cjs
similarity index 97%
rename from index.js
rename to builder.cjs
index 5738e21..061ea2d 100644
--- a/index.js
+++ b/builder.cjs
@@ -287,6 +287,8 @@ module.exports = class Hyperschema {
     this.initializing = false
   }
 
+  static esm = false
+
   _getFullyQualifiedName (description) {
     if (description.namespace === null) return description.name
     return '@' + description.namespace + '/' + description.name
@@ -344,11 +346,16 @@ module.exports = class Hyperschema {
     return json
   }
 
-  toCode () {
-    return generateCode(this)
+  toCode ({ esm = this.constructor.esm } = {}) {
+    return generateCode(this, { esm })
   }
 
-  static toDisk (hyperschema, dir) {
+  static toDisk (hyperschema, dir, opts) {
+    if (typeof dir === 'object' && dir) {
+      opts = dir
+      dir = null
+    }
+
     if (!dir) dir = hyperschema.dir
     fs.mkdirSync(dir, { recursive: true })
 
@@ -356,7 +363,7 @@ module.exports = class Hyperschema {
     const codePath = p.join(p.resolve(dir), CODE_FILE_NAME)
 
     fs.writeFileSync(jsonPath, JSON.stringify(hyperschema.toJSON(), null, 2), { encoding: 'utf-8' })
-    fs.writeFileSync(codePath, hyperschema.toCode(), { encoding: 'utf-8' })
+    fs.writeFileSync(codePath, hyperschema.toCode(opts), { encoding: 'utf-8' })
   }
 
   static from (json) {
diff --git a/builder.mjs b/builder.mjs
new file mode 100644
index 0000000..46dcb4d
--- /dev/null
+++ b/builder.mjs
@@ -0,0 +1,7 @@
+import Hyperschema from './builder.cjs'
+
+class ESMHyperschema extends Hyperschema {
+  static esm = true
+}
+
+export default ESMHyperschema
diff --git a/lib/codegen.js b/lib/codegen.js
index 4092f48..15f6922 100644
--- a/lib/codegen.js
+++ b/lib/codegen.js
@@ -1,7 +1,7 @@
 const gen = require('generate-object-property')
 const s = require('generate-string')
 
-module.exports = function generateSchema (hyperschema) {
+module.exports = function generateSchema (hyperschema, { esm = false } = {}) {
   const structs = []
   const structsByName = new Map()
 
@@ -30,7 +30,13 @@ module.exports = function generateSchema (hyperschema) {
   str += '/* eslint-disable quotes */\n'
   str += '\n'
   str += `const VERSION = ${hyperschema.version}\n`
-  str += 'const { c } = require(\'hyperschema/runtime\')\n'
+
+  if (esm) {
+    str += 'import { c } from \'hyperschema/runtime\')\n'
+  } else {
+    str += 'const { c } = require(\'hyperschema/runtime\')\n'
+  }
+
   str += '\n'
   str += '// eslint-disable-next-line no-unused-vars\n'
   str += 'let version = VERSION\n'
@@ -102,7 +108,14 @@ module.exports = function generateSchema (hyperschema) {
   str += '  }\n'
   str += '}\n'
   str += '\n'
-  str += 'module.exports = { resolveStruct: getStruct, getStruct, getEnum, getEncoding, encode, decode, setVersion, version }\n'
+  str += 'const resolveStruct = getStruct // compat\n'
+  str += '\n'
+
+  if (esm) {
+    str += 'export { resolveStruct, getStruct, getEnum, getEncoding, encode, decode, setVersion, version }\n'
+  } else {
+    str += 'module.exports = { resolveStruct, getStruct, getEnum, getEncoding, encode, decode, setVersion, version }\n'
+  }
 
   return str
 
diff --git a/package.json b/package.json
index cc99f76..ade2ebd 100644
--- a/package.json
+++ b/package.json
@@ -2,12 +2,33 @@
   "name": "hyperschema",
   "version": "1.5.0",
   "description": "Create registries of declarative compact-encoding schemas",
-  "main": "index.js",
   "files": [
-    "lib/**",
-    "index.js",
+    "lib/*.js",
+    "builder.js",
+    "builder.cjs",
+    "runtime.cjs",
     "runtime.js"
   ],
+  "exports": {
+    ".": {
+      "import": "./builder.mjs",
+      "default": "./builder.cjs"
+    },
+    "./runtime": {
+      "import": "./runtime.mjs",
+      "default": "./runtime.cjs"
+    }
+  },
+  "imports": {
+    "fs": {
+      "bare": "bare-fs",
+      "default": "fs"
+    },
+    "path": {
+      "bare": "bare-path",
+      "default": "path"
+    }
+  },
   "scripts": {
     "test": "standard && brittle test/index.js",
     "test:bare": "standard && bare test/index.js"
@@ -28,16 +49,6 @@
     "generate-object-property": "^2.0.0",
     "generate-string": "^1.0.1"
   },
-  "imports": {
-    "fs": {
-      "bare": "bare-fs",
-      "default": "fs"
-    },
-    "path": {
-      "bare": "bare-path",
-      "default": "path"
-    }
-  },
   "devDependencies": {
     "brittle": "^3.7.0",
     "standard": "^17.1.0",
diff --git a/runtime.js b/runtime.cjs
similarity index 100%
rename from runtime.js
rename to runtime.cjs
diff --git a/runtime.mjs b/runtime.mjs
new file mode 100644
index 0000000..4e646e7
--- /dev/null
+++ b/runtime.mjs
@@ -0,0 +1,3 @@
+import compact from 'compact-encoding'
+
+export const c = compact
diff --git a/test/helpers/index.js b/test/helpers/index.js
index f273f1e..8b0899f 100644
--- a/test/helpers/index.js
+++ b/test/helpers/index.js
@@ -2,7 +2,7 @@ const p = require('path')
 const fs = require('fs')
 const tmp = require('test-tmp')
 
-const Hyperschema = require('../..')
+const Hyperschema = require('../../builder.cjs')
 
 class TestBuilder {
   constructor (dir, test) {
@@ -37,9 +37,9 @@ async function makeDir (t) {
   const dir = await tmp(t, { dir: p.join(__dirname, '../test-storage') })
 
   // Copy the runtime into the tmp dir so that we don't need to override it in the codegen
-  const runtimePath = p.join(dir, 'node_modules', 'hyperschema', 'runtime.js')
+  const runtimePath = p.join(dir, 'node_modules', 'hyperschema', 'runtime.cjs')
   await fs.promises.mkdir(p.dirname(runtimePath), { recursive: true })
-  await fs.promises.copyFile(p.resolve(dir, '../../../runtime.js'), runtimePath)
+  await fs.promises.copyFile(p.resolve(dir, '../../../runtime.cjs'), runtimePath)
   return dir
 }