In most navies of the world, a Fleet Admiral is a senior Admiral in command of a large group of ships, comprising a Fleet or, in some cases, a group of Fleets.

Fleet Admiral was also the name of a thoroughbred race horse.

In the United States Navy, a Fleet Admiral is considered the equivalent of a five-star general. The United States rank of Fleet Admiral was created in 1944 and was held during the Second World War by William F. Halsey, Ernest J. King, William D. Leahy, and Chester W. Nimitz.

The insignia for Fleet Admiral comprises five stars in a pentagon design with a thick rank strip, below four smaller stripes, on the service dress blue uniform. The United States Army equivalent to Fleet Admiral is known as General of the Army.

Since the close of the Second World War, there have been no additional Fleet Admirals appointed in the United States Navy. However, the rank still remains listed on offical U.S. rank insignia precedence charts and could be restablished at the discretion of the United States Congress.

U.S. Naval tradition holds that the rank Admiral of the Navy is considered senior to that of Fleet Admiral. The only person to ever hold the rank of Admiral of the Navy was George Dewey.

The modern day German Navy does not have a rank equivalent to that of Fleet Admiral. However, during the Second World War, the equivalent of Fleet Admiral was known in the Kriegsmarine as Grand Admiral.

Karl Donitz, Commander of the U-Boat Fleet and later successor to Adolf Hitler was a German Grand Admiral.

The Kreigsmarine also used the odd titled rank "General Admiral" which was considered senior to a full Admiral, but junior to a Grand Admiral.

In the British Royal Navy, the rank of Fleet Admiral is refered to as Admiral of the Fleet. 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 sqaudron 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.

The Turkish Navy refers to the rank of Fleet Admiral as "Buyukamiral". The sleeve insignia is identicial to that of the British Navy, upon which the rank was based, however the shoulder board of a Turkish Fleet Admiral displays an extensively elaborate design.

The modern Russian Navy maintains a senior Naval rank known as Fleet Admiral of the Russian Federation. The rank is the equivalent of the Soviet rank "Admiral of the Fleet of the Soviet Union" and uses a very similar insignia

During the reign of Saddam Hussein, the Iraqi Navy maintained a Fleet Admiral rank known as Mushir. A Mushir was the senior of all Naval officers and the rank was rarely bestowed. The sleeve insignia of a Mushir was the same as a British Admiral of the Fleet.

The highest rank on the Republic of Korea Navy is known as Wong-Su. The rank exists on paper only, and has never been held by an officer of the South Korean Navy. It is theorized that the rank could be bestowed in the event of another major war with North Korea; however, such a rank would only be issued in the event of a prolonged conflict.

The rank insignia for Wong-Su is heavily influenced by United States military insignia, in that a five star pentagon design is used very similar to the U.S. rank of General of the Army