An amphibious assault ship (also referred to as a commando carrier or an amphibious assault carrier) is a type of amphibious warfare ship employed to land and support ground forces on enemy territory by an amphibious assault. The design evolved from aircraft carriers converted for use as helicopter carriers, but includes support for amphibious landing craft, with most designs including a well deck. Coming full circle, some amphibious assault ships now have a secondary role as aircraft carriers, supporting V/STOL fixed-wing aircraft.

The role of the amphibious assault ship is fundamentally different from a standard aircraft carrier: its aviation facilities have the primary role of hosting helicopters to support forces ashore rather than to support strike aircraft. However, some are capable of serving in the sea-control role, embarking aircraft like Harrier fighters for CAP and anti-submarine warfare helicopters or operating as a safe base for large numbers of STOVL fighters conducting air support for the Marine expeditionary unit once it has gone ashore. Most of these ships can also carry or support landing craft, such as air-cushioned landing craft (hovercraft) or LCUs.

Amphibious warfare is a type of offensive military operation that today uses naval ships to project ground and air power onto a hostile or potentially hostile shore at a designated landing beach. Through history the operations were conducted using ship's boats as the primary method of delivering troops to shore. Since the Gallipoli Campaign specialised watercraft were increasingly designed for landing troops, materiel and vehicles, including by landing craft and for insertion of commandos, by fast patrol boats, zodiacs (rigid inflatable boats) and from mini-submersibles.

The term amphibious first emerged in the USA during the 1930s after design of the Landing Vehicle Tracked where the first prototypes were named Alligator and Crocodile, though neither species are amphibian. Amphibious warfare includes operations defined by their type, purpose, scale and means of execution. In the British Empire at the time these were called combined operations which were defined as "...operations where naval, military or air forces in any combination are co-operating with each other, working independently under their respective commanders, but with a common strategic object." All armed forces that employ troops with special training and equipment for conducting landings from naval vessels to shore agree to this definition.