The Free Territory of Trieste was an independent territory in Southern Europe between Italy and Yugoslavia, facing the north part of the Adriatic Sea, under direct responsibility of the United Nations Security Council in the aftermath of World War II. It acted as such for a period of seven years.

The territory was established on 10 February 1947, by a protocol of the Treaty of Peace with Italy, to accommodate an ethnically and culturally mixed population in a neutral independent country. The intention was also to cool down territorial claims between Italy and Yugoslavia, due to its strategic importance for trade with Central Europe. It came into existence on 15 September 1947. Its administration was divided into two areas: one being the port city of Trieste with a narrow coastal strip to the northwest (Zone A); the other (Zone B) was formed by a small portion of the north-western part of the Istrian peninsula.

The territory was de facto dissolved in 1954 and given to Italy (Zone A) and Yugoslavia (Zone B). This created a border dispute which was only settled twenty years later with the signing of the bilateral Treaty of Osimo in 1975, which was ratified in 1977.

The city of Trieste and the territory of Zone A is today under the control of Italy and its Friuli-Venezia Giulia region. Following the dissolution of Yugoslavia in the early 1990s, the area of Zone B is today under the control of Slovenia and Croatia.

The Free Territory of Trieste comprised an area of 738 square kilometres (285 sq mi) around the Gulf of Trieste in the northern Adriatic, from Duino (Devin) in the north to Cittanova (Novigrad) in the south, and had approximately 330,000 inhabitants.

It bordered post-war Italy to the north, and Yugoslavia to the east and south. The rivers of the territory included the Rižana/Risano, the Dragonja/Dragogna, the Timavo/Timava, the Val Rosandra/Glinščica, and the Mirna/Quieto. The Territory's highest point was at Monte Cocusso/Kokoš (668 metres (2,192 ft)). Its most extreme points were near Medeazza/Medjavas at 45° 48’ in the north, at Tarski Zaliv / Porto Quieto at 45° 18’ in the south, Savudrija / Punta Salvore at 13° 29’ in the west, and Gročana/Grozzana at 13° 55’ in the east.

Since 1382, Trieste had been part of the Habsburg monarchy, whereas neighboring Istria had been divided for centuries between the Habsburg monarchy (its central, northern and eastern parts) and the Republic of Venice (its western and southern parts). The population of the territory has been diverse and mixed, with different and often changing ethnic majorities in different parts of the territory.^{[citation needed]}

Italian-speakers have been predominant in most urban settlements and along the coast, with significant ethnic Slavic minorities of Slovenes and Croats inland – especially in the Trieste district, where Slovenes represented a third of the population by the end of World War I (although most of them were recent arrivals, after 1880, from interior Slovene districts). The countryside of the territory was mostly populated by ethnic Slovenes or Croats in the southernmost portion of the area. There were also smaller numbers of Istro-Romanians, Greeks, Albanians, as well as a sizeable Triestine Jewish community.