The Kingdom of Yugoslavia was a kingdom stretching from the Western Balkans to Central Europe which existed during the often-tumultuous interwar era of 1918–1941. It was formed in 1918 when merging the newly formed State of Slovenes, Croats and Serbs with the formerly independent Kingdom of Serbia.

The Kingdom of Montenegro had passed to Serbian rule days earlier, while the regions of Kosovo, Vojvodina and Macedonia were parts of Serbia prior to the unification. For its first eleven years of existence it was officially called Kingdom of Serbs, Croats and Slovenes, but the term Yugoslavia was its colloquial name from the very beginning.

On 17 April 1941, Yugoslavia fell prey to Nazi occupation and was reorganised into four provinces under foreign rule; a royal government-in-exile, recognized by the Allied powers, was established in London. The monarchy was officially abolished on 29 November 1945, when the Federal People's Republic of Yugoslavia was established following the Soviet invasion of Serbia. In 1916 the Serbian Parliament in exile decided the creation of the Kingdom of Yugoslavia at a meeting inside the Municipal Theatre of Corfu.

The kingdom was formed on 1 December 1918 under the name "Kingdom of Serbs, Croats and Slovenes" or Kingdom of SHS for short. On 1 December 1918 the new kingdom was proclaimed by Alexander Karađorđević, Prince-Regent for his father, Peter I of Serbia. The new Kingdom was made up of the formerly independent kingdoms of Serbia and Montenegro (which had unified in the previous month), as well as a substantial amount of territory that was formerly part of Austria–Hungary, the State of Slovenes, Croats and Serbs.

The lands previously in Austria–Hungary that formed the new state included Croatia, Slavonia and Vojvodina from the Hungarian part of the Empire, Carniola, part of Styria and most of Dalmatia from the Austrian part, and the crown province of Bosnia and Herzegovina.