Napalm is an incendiary mixture of a gelling agent and a volatile petrochemical (usually petrol or diesel fuel). The name is a portmanteau of two of the constituents of the original thickening and gelling agents: coprecipitated aluminium salts of naphthenic acid and palmitic acid. Napalm B is the more modern version of napalm (utilizing polystyrene derivatives) and, although distinctly different in its chemical composition, is often referred to simply as "napalm". A team led by chemist Louis Fieser originally developed napalm for the US Chemical Warfare Service in 1942 in a secret laboratory at Harvard University. Of immediate first interest was its viability as an incendiary device to be used in fire bombing campaigns during World War II; its potential to be coherently projected into a solid stream that would carry for distance (instead of the bloomy fireball of pure gasoline) resulted in widespread adoption in infantry flamethrowers as well.

Napalm burns at temperatures ranging from 800 to 1,200 °C (1,470 to 2,190 °F). It burns longer than gasoline, is more easily dispersed, and adheres to its targets. These traits make it effective and controversial. It has been widely deployed from the air and from the ground, the largest use being via airdropped bombs in World War II in the incendiary attacks on Japanese cities in 1945. It was used also for close air support roles in the First Indochina War, the Korean War and the Second Indochina War. Napalm also has fueled most of the flamethrowers (tank-, ship-, and infantry-based) used since World War II, giving them much greater range, and was a common weapon of urban combat by both the Axis and the Allies in World War II.