diff --git a/index.d.ts b/index.d.ts
new file mode 100644
index 0000000..7290789
--- /dev/null
+++ b/index.d.ts
@@ -0,0 +1,30 @@
+export type Change<S, M> = [S, Effect<M>?];
+
+export interface Effect<M> {
+  (dispatch: Dispatch<M>): void;
+}
+
+export interface Update<M, S> {
+  (message: M, state: S): Change<S, M>;
+}
+
+export interface View<M, S, V> {
+  (state: S, dispatch: Dispatch<M>): V;
+}
+
+export interface Dispatch<M> {
+  (message: M): void;
+}
+
+export interface Done<S> {
+  (state: S): void;
+}
+
+export interface Program<S, M, V> {
+  readonly init: Change<S, M>;
+  readonly update: Update<M, S>;
+  readonly view: View<M, S, V>;
+  readonly done?: Done<S>;
+}
+
+export function runtime<S, M, V>(program: Program<S, M, V>): void;
diff --git a/package.json b/package.json
index f4e5fcf..ad2f3e7 100644
--- a/package.json
+++ b/package.json
@@ -29,5 +29,6 @@
   "scripts": {
     "lint": "fixpack && prettier index.js test/**/*.js --write && standard --fix",
     "test": "npm run lint && ava"
-  }
+  },
+  "types": "index.d.ts"
 }