In the past, bombers were an obvious separate type, and often looked dramatically different from other types as well. This was due largely to the lack of power in aircraft engines, meaning that in order to carry any reasonable warload, the designs had to carry multiple engines. The result was a much larger aircraft, one with a reasonable useful load fraction for the role. Engine power was so scarce that designs had to be tailored to one particular niche; during World War II there were dive bombers, light, medium and heavy bombers, and specialized ground attack designs.

Traditionally, bombers have carried only defensive armament, and are not designed to engage in combat with other aircraft. They are relatively large and unmaneuverable (although some have been as fast or faster than contemporary fighters). Attack aircraft are smaller, faster, and more agile, but less so than a fighter when armed for a ground attack mission. They may carry air-to-air armament, but typically only for self-defense.

In modern air forces, the distinction between bombers, fighter-bombers, and attack aircraft has become blurry. Many attack aircraft, even ones that look like fighters, are optimized to drop bombs, with very little ability to engage in aerial combat. Indeed, the design qualities that make an effective low-level attack aircraft make for a distinctly inferior air superiority fighter, and vice versa. Conversely, many fighter aircraft, such as the F-16, are often used as 'bomb trucks,' despite being designed for aerial combat. Perhaps the one meaningful distinction at present is the question of range: a bomber is generally a long-range aircraft capable of striking targets deep within enemy territory, whereas fighter bombers and attack aircraft are limited to 'theater' missions in and around the immediate area of battlefield combat. Even that distinction is muddied by the availability of aerial refueling, which greatly increases the potential radius of combat operations.

The development of large strategic bombers stagnated in the later part of the Cold War both because of spiraling costs and the advent of the intercontinental ballistic missile, which was felt to have equal deterrent value while being much more difficult to intercept. The United States Air Force XB-70 Valkyrie program was cancelled for that reason in the early 1960s, and the later B-1 Lancer and B-2 Spirit aircraft entered service only after protracted political and development problems. Their high cost meant that few were built and the 1950s-designed B-52s continued in use into the 21st century. Similarly, the Soviet Union fielded the intermediate-range Tupolev Tu-22M in the 1970s, but the Mach 3 bomber project came to naught. The Mach 2 Tupolev Tu-160 was built only in tiny numbers, leaving the earlier Tupolev Tu-16 and Tupolev Tu-95 heavy bombers of 1950s vintage to soldier on into the 21st century. Meanwhile, the British strategic bombing force largely came to an end with the phase-out of the V Bomber force (the last of which left service in 1983. The only other nation that fields a strategic bombing force at present is the People's Republic of China, which has a number of Chinese-built Tupolev Tu-16s.

Plans in the US and Russia for successors to the current strategic bomber force remain only paper projects, and present political and funding pressures suggest that they are likely to for the foreseeable future. In the US, current plans call for the existing USAF bomber fleet to remain in service until the mid-to-late 2020s, with no replacement in sight.

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