diff --git a/when/when.d.ts b/when/when.d.ts
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--- /dev/null
+++ b/when/when.d.ts
@@ -0,0 +1,64 @@
+// Type definitions for When 2.4.0
+// Project: https://github.com/cujojs/when
+// Definitions: https://github.com/borisyankov/DefinitelyTyped
+
+declare module When {
+
+    /**
+     * Return a promise that will resolve only once all the supplied promisesOrValues
+     * have resolved. The resolution value of the returned promise will be an array
+     * containing the resolution values of each of the promisesOrValues.
+     * @memberOf when
+     *
+     * @param promisesOrValues array of anything, may contain a mix
+     *      of {@link Promise}s and values
+     */
+    function all<T>(promisesOrValues: any[]): Promise<T>;
+
+    /**
+     * Creates a {promise, resolver} pair, either or both of which
+     * may be given out safely to consumers.
+     * The resolver has resolve, reject, and progress.  The promise
+     * has then plus extended promise API.
+     */
+    function defer<T>(): Deferred<T>;
+
+    /**
+     * Joins multiple promises into a single returned promise.
+     * @return a promise that will fulfill when *all* the input promises
+     * have fulfilled, or will reject when *any one* of the input promises rejects.
+     */
+    function join<T>(...promises: Promise<T>[]): Promise<T[]>;
+    /**
+     * Joins multiple promises into a single returned promise.
+     * @return a promise that will fulfill when *all* the input promises
+     * have fulfilled, or will reject when *any one* of the input promises rejects.
+     */
+    function join<T>(...promises: any[]): Promise<T[]>;
+
+    /**
+     * Returns a resolved promise. The returned promise will be
+     *  - fulfilled with promiseOrValue if it is a value, or
+     *  - if promiseOrValue is a promise
+     *    - fulfilled with promiseOrValue's value after it is fulfilled
+     *    - rejected with promiseOrValue's reason after it is rejected
+     */
+    function resolve<T>(promise: Promise<T>): Promise<T>;
+    function resolve<T>(value?: T): Promise<T>;
+
+    interface Deferred<T> {
+        notify(update: any): void;
+        promise: Promise<T>;
+        reject(reason: any): void;
+        resolve(value?: T): void;
+    }
+
+    interface Promise<T> {
+        ensure(onFulfilledOrRejected: Function): Promise<T>;
+
+        then<U>(onFulfilled: (value: T) => Promise<U>, onRejected?: (reason: any) => Promise<U>, onProgress?: (update: any) => void): Promise<U>;
+        then<U>(onFulfilled: (value: T) => Promise<U>, onRejected?: (reason: any) => U, onProgress?: (update: any) => void): Promise<U>;
+        then<U>(onFulfilled: (value: T) => U, onRejected?: (reason: any) => Promise<U>, onProgress?: (update: any) => void): Promise<U>;
+        then<U>(onFulfilled: (value: T) => U, onRejected?: (reason: any) => U, onProgress?: (update: any) => void): Promise<U>;
+    }
+}