The Combined Chiefs of Staff (CCS) was the supreme military command for the western Allies during World War II. It was a body constituted from the British Chiefs of Staff Committee and the United States Joint Chiefs of Staff.

Formed in February 1942, the CCS usually held its meetings in Washington. Since the British military chiefs could not be expected to be continually present thousands of miles away from their own capital, the British Joint Staff Mission was a body permanently assigned to Washington to represent British interests. The full CCS usually met only during the great wartime conferences on grand strategy, such as at Casablanca.

Although it was responsible to the joint control of the British and US governments, the CCS controlled forces from many different countries in all theatres, including the Pacific, India and North Africa. The degree of integration between the western militaries that the CCS achieved has never been equalled or surpassed in military history when considering an alliance between sovereign nations.