A medium bomber is a bomber aircraft designed to operate with medium bomb loads over medium distances; primarily to distinguish them from the much larger heavy bombers and smaller light bombers. The term was used primarily prior to and during World War II, when engine power was so scarce that designs had to be carefully tailored to their missions. The medium bomber was generally considered to be any design that delivered about 4,000 lb (1.8 t) over ranges of about 1,500 to 2,000 miles (2,400 to 3,200 km). Heavy bombers were those with a nominal load of 8,000 lb (3.6 t) or more, and light bombers carried 2,000 lb (0.9 t) loads. These distinctions were already disappearing by the middle of WWII, when the average fighter aircraft could now carry a 2,000 lb (0.9 t) load and ever more powerful engines allowed "light" designs to largely take over the missions formerly filled by mediums.

After the war the term disappeared from use almost instantly. Although a number of aircraft were designed in this performance range, they were now almost universally referred to as tactical bombers instead. Famous examples of post-war mediums include the English Electric Canberra (as well as its US counterpart, the Martin B-57) and Ilyushin Il-28 Beagle.

Examples:

Heinkel He 111
- considered a heavy by the Luftwaffe
Junkers Ju 88
B-25 Mitchell
B-26 Marauder
Vickers Wellington
Bristol Beaufort
de Havilland Mosquito
- started as a light bomber, but increasing capacity made it one of the world's best mediums by the end of the war