The Armistice of Cassibile was an armistice signed on 3 September 1943 and made public on 8 September between the Kingdom of Italy and the Allies during World War II.

It was signed by Major General Walter Bedell Smith for the Allies and Brigade General Giuseppe Castellano for Italy at a conference of generals from both sides in an Allied military camp at Cassibile, in Sicily, which had recently been occupied by the Allies. The armistice was approved by both the Italian King Victor Emmanuel III and Marshal Badoglio, the Prime Minister of Italy at the time.

Germany moved rapidly by freeing Benito Mussolini (12 September) and attacking Italian forces in Italy (819 September), southern France and the Balkans. The Italian forces were quickly defeated, and most of Italy was occupied by German troops, who established a puppet state, the Italian Social Republic. The king, the Italian government, and most of the navy escaped to territories occupied by the Allies.

The Allied invasion of Italy was the Allied amphibious landing on mainland Italy that took place from 3 September 1943, during the Italian campaign of World War II. The operation was undertaken by General Sir Harold Alexander's 15th Army Group (comprising General Mark W. Clark's American Fifth Army and General Bernard Montgomery's British Eighth Army) and followed the successful Allied Invasion of Sicily. The main invasion force landed around Salerno on 9 September on the western coast in Operation Avalanche, while two supporting operations took place in Calabria (Operation Baytown) and Taranto (Operation Slapstick).