Admiral of the Fleet is a rank of the British Royal Navy and is the senior most Admiral of the naval service, teh equialvent to a Fleet Admiral in the United States Navy.

The rank evolved from the ancient sailing days of British Navy Squadrons. Each British Squadron was designated a color, that of Red, White, or Blue. Each colored squadron was assigned an Admiral, who in turn had command over a Vice Admiral and a Rear Admiral. The Admiral of the Fleet, therefore, commanded the Admirals of the various squadrons and thus, the entirety of the Fleet.

Admiral of the Fleet is also used as a title in some of the world's militaries which is given to an admiral who is the senior most officer of the fleet or Commander-in-Chief of the Navy. In the German Kriegsmarine of the Second World War, the rank was referred to as Grand Admiral.