Firebombing is a bombing technique designed to damage a target, generally an urban area, through the use of fire, caused by incendiary devices, rather than from the blast effect of large bombs. In popular usage, any act in which an incendiary device is used to initiate a fire is often described as a "firebombing".

Although simple incendiary bombs have been used to destroy buildings since the start of gunpowder warfare, World War I saw the first use of strategic bombing from the air to damage the morale and economy of the enemy, such as the German Zeppelin air raids conducted on London. The Chinese wartime capital of Chongqing was firebombed by the Imperial Japanese starting in early 1939 during the Second Sino-Japanese War. London, Coventry, and many other British cities were firebombed during the Blitz by Nazi Germany. Most large German cities were extensively firebombed starting in 1942, and almost all large Japanese cities were firebombed during the last six months of World War II.

This technique makes use of small incendiary bombs possibly delivered by a cluster bomb, such as the Molotov bread basket. If a fire catches, it could spread, taking in adjacent buildings that would have been largely unaffected by a high explosive bomb. This is a more effective use of the payload that a bomber could carry.

The use of incendiaries alone does not generally start uncontrollable fires where the targets are roofed with nonflammable materials such as tiles or slates. The use of a mixture of bombers carrying high explosive bombs, such as the British blockbuster bombs, which blew out windows and roofs and exposed the interior of buildings to the incendiary bombs, is much more effective. Alternatively, a preliminary bombing with conventional bombs can be followed by subsequent attacks by incendiary carrying bombers.

A large part of the success of this particular type of bomb is because of its tendency to start infernos and cause major damage to houses around it which would traditionally be made using wood and cardboard.

Early in World War II many British cities were firebombed. Two particularly notable raids were the Coventry Blitz on 14 November 1940, and the blitz on London on the night of 29 December/30 December 1940, which was the most destructive raid on London during the war with much of the destruction caused by fires started by incendiary bombs. During the Coventry Blitz the Germans pioneered several innovations which were to influence all future strategic bomber raids during the war. These were: the use of pathfinder aircraft with electronic aids to navigate, to mark the targets before the main bomber raid; and the use of high explosive bombs and air-mines coupled with thousands of incendiary bombs intended to set the city ablaze. The first wave of follow-up bombers dropped high explosive bombs, the intent of which was to knock out the utilities (the water supply, electricity network and gas mains), and to crater the road — making it difficult for the fire engines to reach fires started by the successive waves of bombers. The follow-up waves dropped a combination of high explosive and incendiary bombs. There were two types of incendiary bombs: those made of magnesium and iron powders, and those made of petroleum. The high-explosive bombs and the larger air-mines were not only designed to hamper the Coventry fire brigade, they were also intended to damage roofs, making it easier for the incendiary bombs to fall into buildings and ignite them. As Sir Arthur Harris, commander of RAF Bomber Command, wrote after the war:

In the early days of bombing our notion, like that of the Germans, was to spread an attack out over the whole night, thereby wearing down the morale of the civilian population. The result was, of course, that an efficient fire brigade could tackle a single load of incendiaries, put them out, and wait in comfort for the next to come along; they might also be able to take shelter when a few high explosives bombs were dropping. ... But it was observed that when the Germans did get an effective concentration, ... then our fire brigades had a hard time; if a rain of incendiaries is mixed with high explosives bombs there is a temptation for the fireman to keep his head down. The Germans, again and again, missed their chance, as they did during the London blitz that I watched from the roof of the Air Ministry, of setting our cities ablaze by a concentrated attack. Coventry was adequately concentrated in point of space, but all the same, there was little concentration in point of time, and nothing like the fire tornadoes of Hamburg or Dresden ever occurred in this country. But they did do us enough damage to teach us the principle of concentration, the principle of starting so many fires at the same time that no firefighting services, however efficiently and quickly they were reinforced by the fire brigades of other towns could get them under control.

— Arthur Harris