diff --git a/which/which-tests.ts b/which/which-tests.ts
new file mode 100644
index 0000000000..45a376dcb3
--- /dev/null
+++ b/which/which-tests.ts
@@ -0,0 +1,10 @@
+/// <reference path="./which.d.ts" />
+
+import which = require("which");
+
+which("cat", (err, path) => {
+  console.log(path);
+});
+
+var path = which.sync("cat");
+console.log(path);
diff --git a/which/which.d.ts b/which/which.d.ts
new file mode 100644
index 0000000000..d25ac4fd7f
--- /dev/null
+++ b/which/which.d.ts
@@ -0,0 +1,13 @@
+// Type definitions for which 1.0.8
+// Project: https://github.com/isaacs/node-which
+// Definitions by: vvakame <https://github.com/vvakame>
+// Definitions: https://github.com/borisyankov/DefinitelyTyped
+
+declare module "which" {
+  function when (cmd: string, cb: (err: Error, path: string) => void): void;
+  module when {
+    function sync(cmd: string): string;
+  }
+
+  export = when;
+}