Blitz, The, sustained German bombing campaign against London and other British cities during World War II, from September 1940 to mid-1941, in which over 43,000 British citizens lost their lives. The Blitz was named after the German blitzkrieg strategy of mobile offensive warfare, though it was not a specific example of this. Since the end of World War II the Blitz has been celebrated in popular British culture as an example of the courage and resilience of the British people, and of Londoners in particular, during a crucial period when the British Isles stood alone against the might of the German armed forces, the Wehrmacht.

While the Battle of Britain was still in progress the Germans had refrained from attacking civilian targets, concentrating instead upon the destruction of the Royal Air Force (RAF). Nevertheless, a limited bombing campaign against industrial and communications installations had been under way since mid-August 1940. On the night of August 24, 1940, German bombers originally bound for the oil refineries at Thames Haven drifted off course and dropped their loads on central London. An escalation of the air war immediately set in on both sides. Winston Churchill ordered retaliatory attacks against Berlin, and the Germans responded by launching further raids on London and Liverpool. On September 7, the commander-in-chief of the Luftwaffe (German air force), Hermann Göring, launched a huge daylight raid on the East End of London which left 430 dead, over 1,600 seriously injured, and thousands more homeless. Thereafter his bombers returned to London on 57 consecutive nights. The German aims were to disrupt war production and communications, paralyse the British economy, and, not least, to instil terror in the civilian population. However, although London's defences were hardly equipped to repel a major air offensive, the Germans themselves lacked a strategic bomber force capable of conducting an independent air war over Britain. Their crews, too, lacked the required training and, although damage to property and loss of life were extensive, the Blitz statistics pale into insignificance when compared to those of the later Allied raids on Hamburg and Dresden. The counter-attack by the RAF took a heavy toll of attacking bombers, though not enough to halt the German raids; by the autumn of 1940 British air defences were destroying German bombers faster than the Germans could build them, showing that Germany could not win a prolonged aerial campaign over Britain. Anti-aircraft batteries, and barrage balloons against low-flying bombers supplemented the efforts of the Spitfires and Hurricanes of the RAF's Fighter Command.

Gradually the Germans extended the scope of their operations and targeted numerous other cities, including Coventry, Manchester, Plymouth, Bristol, Glasgow, and Belfast. Nevertheless, London bore the brunt of the attacks from September 1940 to May of the following year. Although British propaganda insisted that Britain could “take it”, a phrase popularized by Churchill during the Blitz, the disruption of industry and commerce caused by the bombing was considerable. The rituals of air raid drill, patrols by warders, blackouts in which streetlights were extinguished and windows heavily curtained to deny German bombers aiming points, and taping of windows to prevent glass flying in a bomb explosion, became part of the pattern of daily life under constant threat of attack. Morale among the civilians, too, was not as strong as it was portrayed in contemporary British propaganda. Exhaustion, lack of sleep, fear, and bereavement all took their toll. Indeed, many chose to flee the capital, and by November 1940 the population of central London had dropped by 25 per cent. Children, in particular, were evacuated from the endangered cities to remoter areas, a relocation that in some cases would last for years. Those for whom evacuation or flight were not serious options, particularly the population of the deprived East End districts, sought shelter from the bombing in the stations of the London underground, from which some people did not emerge for weeks on end. The authorities, who had originally wished to prevent recourse to such measures, soon found themselves powerless in the face of overwhelming public pressure.

Though British cities continued to suffer heavy raids in the winter of 1940 and well into 1941, the Blitz had lost its original strategic purpose—preparatory bombardment heralding a full-scale German invasion across the English Channel—in September 1940, when Adolf Hitler suspended Operation Sea Lion (his invasion plan) following RAF bomber attacks on invasion forces in occupied France. The Luftwaffe switched from daylight to night bombing after September, acknowledging their failure to gain air superiority. By enduring the Blitz, Britain's civilians at least eased German pressure on RAF bases, and ensured Britain's victory in the Battle of Britain.

The London Blitz finally ended with an extremely heavy raid on May 10, 1941. Almost 1,500 people were killed, the House of Commons was severely damaged, and over 2,000 fires raged over a wide area of the capital. In the following weeks smaller attacks continued on London and other cities, but by the early summer of 1941 the vast majority of the Luftwaffe's striking power had been redeployed in Eastern Europe prior to the launching of Operation Barbarossa, Adolf Hitler's planned surprise attack on the Union of Soviet Socialist Republics. The Blitz was finally over.