A heavy bomber is a bomber aircraft of the largest size, and typically longest ranges. 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 heavy bomber was generally considered to be any design that delivered 8,000 lb (4 t) of bombs or more on distant targets, with medium bombers having loads of 4,000 to 8,000 lb (2 to 4 t), and light bombers 2,000 to 4,000 lb (1 to 2 t). These distinctions were already disappearing by the middle of WWII, when the average fighter aircraft could now carry a 2,000 lb (1 t) load and the "light" designs had now largely taken over the missions formerly filled by mediums.

After the war the term saw some limited use to describe bombers dedicated to the strategic role, but soon these were being referred to as strategic bombers, while every other design became a tactical bomber. The only aircraft in the world that could still be considered heavy bombers would be the B-52 Stratofortress and, to a lesser degree, B-1 Lancer. The general utility of a manned heavy bomber has been greatly degraded with the introduction of more accurate munitions such as smart bombs, but the B-52 continues to fill a role when the target requires a massive number of bombs to be dropped. It is significant that no other air force fields a heavy bomber.