The Socialist Federal Republic of Yugoslavia (commonly abbreviated as SFRY or SFR Yugoslavia), known from 1945 to 1963 as the Federal People's Republic of Yugoslavia, commonly referred to as Socialist Yugoslavia or simply Yugoslavia, was a country in Central and Southeast Europe. It was established in 1945, following World War II, and lasted until 1992, dissolving amid the onset of the Yugoslav Wars. Spanning an area of 255,804 square kilometres (98,766 sq mi) in the Balkans, Yugoslavia was bordered by the Adriatic Sea and Italy to the west, Austria and Hungary to the north, Bulgaria and Romania to the east, and Albania and Greece to the south. It was a one-party socialist state and federation governed by the League of Communists of Yugoslavia, and had six constituent republics: Bosnia and Herzegovina, Croatia, Macedonia, Montenegro, Serbia, and Slovenia. Within Serbia was the Yugoslav capital city of Belgrade as well as two autonomous Yugoslav provinces: Kosovo and Vojvodina.

The country emerged as Democratic Federal Yugoslavia on 29 November 1943, during the second session of the Anti-Fascist Council for the National Liberation of Yugoslavia midst World War II in Yugoslavia. Recognised by the Allies of World War II at the Tehran Conference as the legal successor state to Kingdom of Yugoslavia, it was a provisionally governed state formed to unite the Yugoslav resistance movement. Following the country's liberation, King Peter II was deposed, the monarchical rule was ended, and on 29 November 1945, the Federal People's Republic of Yugoslavia was proclaimed. Led by Josip Broz Tito, the new communist government sided with the Eastern Bloc at the beginning of the Cold War but pursued a policy of neutrality following the 1948 Tito–Stalin split; it became a founding member of the Non-Aligned Movement, and transitioned from a command economy to market-based socialism. The country was renamed Socialist Federal Republic of Yugoslavia in 1963.

After Tito died on 4 May 1980, the Yugoslav economy began to collapse, which increased unemployment and inflation. The economic crisis led to rising ethnic nationalism and political dissidence in the late 1980s and early 1990s. With the fall of communism in Eastern Europe, efforts to transition into a confederation failed; the two wealthiest republics, Croatia and Slovenia, seceded and gained some international recognition in 1991. The federation dissolved along the borders of federated republics, hastened by the start of the Yugoslav Wars, and formally broke up on 27 April 1992. Two republics, Serbia and Montenegro, remained within a reconstituted state known as the Federal Republic of Yugoslavia, or FR Yugoslavia, but this state was not recognized internationally as the sole successor state to SFR Yugoslavia. "Former Yugoslavia" is now commonly used retrospectively.

The FPR Yugoslavia and, later SFRY, was a founding member of the United Nations, the Non-Aligned Movement and the Organization for Security and Co-operation in Europe.

The name Yugoslavia, an anglicised transcription of Jugoslavija, is a compound word made up of jug ('yug'; with the 'j' pronounced like an English 'y') and slavija. The Slavic word jug means 'south', while slavija ("Slavia") denotes a 'land of the Slavs'. Thus, a translation of Jugoslavija would be 'South-Slavia' or 'Land of the South Slavs'. The federation's official name varied considerably between 1945 and 1992. Yugoslavia was formed in 1918 under the name Kingdom of Serbs, Croats and Slovenes. In January 1929, King Alexander I assumed dictatorship of the kingdom and renamed it the Kingdom of Yugoslavia, for the first time making "Yugoslavia"—which had been used colloquially for decades (even before the country was formed)—the state's official name. After the Axis occupied the kingdom during World War II, the Anti-Fascist Council for the National Liberation of Yugoslavia (AVNOJ) announced in 1943 the formation of the Democratic Federal Yugoslavia (DF Yugoslavia or DFY) in the country's substantial resistance-controlled areas. The name deliberately left the republic-or-kingdom question open. In 1945, King Peter II was officially deposed, with the state reorganized as a republic, and accordingly renamed the Federal People's Republic of Yugoslavia (FPR Yugoslavia or FPRY), with the constitution coming into force in 1946. In 1963, amid pervasive liberal constitutional reforms, the name Socialist Federal Republic of Yugoslavia was introduced. The state is most commonly called by that name, which it held for the longest period. Of the three main Yugoslav languages, the Serbo-Croatian and Macedonian names for the state were identical, while Slovene slightly differed in capitalization and the spelling of the adjective Socialist. The names are as follows:

Due to the name's length, abbreviations were often used for the Socialist Federal Republic of Yugoslavia, though it was most commonly known simply as Yugoslavia. The most common abbreviation is SFRY, though "SFR Yugoslavia" was also used in an official capacity, particularly by the media.

On 6 April 1941, Yugoslavia was invaded by the Axis powers led by Nazi Germany; by 17 April 1941, the country was fully occupied and was soon carved up by the Axis. Yugoslav resistance was soon established in two forms, the Royal Yugoslav Army in the Homeland and the Communist Yugoslav Partisans. The Partisan supreme commander was Josip Broz Tito. Under his command, the movement soon began establishing "liberated territories" that attracted the occupying forces' attention. Unlike the various nationalist militias operating in occupied Yugoslavia, the Partisans were a pan-Yugoslav movement promoting the "brotherhood and unity" of Yugoslav nations and representing the Yugoslav political spectrum's republican, left-wing, and socialist elements. The coalition of political parties, factions, and prominent individuals behind the movement was the People's Liberation Front (Jedinstveni narodnooslobodilački front, JNOF), led by the Communist Party of Yugoslavia (KPJ).

The Front formed a representative political body, the Anti-Fascist Council for the People's Liberation of Yugoslavia (AVNOJ, Antifašističko Veće Narodnog Oslobođenja Jugoslavije). The AVNOJ met for the first time in Partisan-liberated Bihać on 26 November 1942 (First Session of the AVNOJ) and claimed the status of Yugoslavia's deliberative assembly (parliament).