The Yugoslav Partisans, or the National Liberation Army, officially the National Liberation Army and Partisan Detachments of Yugoslavia, was the Communist-led Anti-fascist resistance to the Axis powers (chiefly Germany) in occupied Yugoslavia during World War II. Led by Josip Broz Tito, the Partisans are considered to be Europe's most effective anti-Axis resistance movement during World War II.Primarily a guerilla force at its inception, the Partisans developed into a large fighting force engaging in conventional warfare later in the war, numbering around 650,000 in late 1944 and organized in four field armies and 52 divisions. The main stated objectives of the Partisans were the liberation of Yugoslav lands from occupying forces and the creation of a federal, multi-ethnic socialist state in Yugoslavia.

The Partisans were organized on the initiative of Tito following the Axis invasion of Yugoslavia in April 1941, and began an active guerrilla campaign against occupying forces after Germany invaded the Soviet Union in June. A large-scale uprising was launched in July, later joined by Draža Mihailović's Chetniks, which led to the creation of the short-lived Republic of Užice. The Axis mounted a series of offensives in response but failed to completely destroy the highly mobile Partisans and their leadership. By late 1943 the Allies had shifted their support from Mihailović to Tito as the extent of Chetnik collaboration became evident, and the Partisans received official recognition at the Tehran Conference. In Autumn 1944, the Partisans and the Soviet Red Army liberated Belgrade following the Belgrade Offensive. By the end of the war, the Partisans had gained control of the entire country as well as Trieste and Carinthia. After the war, the Partisans were reorganized into the regular armed force of the newly established Federal People's Republic of Yugoslavia.