A neutron bomb, officially defined as a type of enhanced radiation weapon (ERW), is a low-yield thermonuclear weapon designed to maximize lethal neutron radiation in the immediate vicinity of the blast while minimizing the physical power of the blast itself. The neutron release generated by a nuclear fusion reaction is intentionally allowed to escape the weapon, rather than being absorbed by its other components. The neutron burst, which is used as the primary destructive action of the warhead, is able to penetrate enemy armor more effectively than a conventional warhead, thus making it more lethal as a tactical weapon.

The concept was originally developed by the United States in the late 1950s and early 1960s. It was seen as a "cleaner" bomb for use against massed Soviet armored divisions. As these would be used over allied nations, notably West Germany, the reduced blast damage was seen as an important advantage.

ERWs were first operationally deployed for anti-ballistic missiles (ABMs). In this role the burst of neutrons would cause nearby warheads to undergo partial fission, preventing them from exploding properly. For this to work, the ABM would have to explode within approximately 100 metres (300 ft) of its target. The first example of such a system was the W66, used on the Sprint missile used in the US Nike-X system. It is believed the Soviet equivalent, the A-135's 53T6 missile, uses a similar design.

The weapon was once again proposed for tactical use by the United States in the 1970s and 1980s, and production of the W70 began for the MGM-52 Lance in 1981. This time it led to protests as the growing anti-nuclear movement gained strength through this period. Opposition was so intense that European leaders refused to accept it on their territory. US President Ronald Reagan ordered the production of the W70-3, which remained in the US stockpile until they were retired in 1992. The last W70 was dismantled in February 1996.