The Socialist Republic of Bosnia and Herzegovina (SR Bosnia and Herzegovina; Serbo-Croatian: Socijalistička Republika Bosna i Hercegovina / Социјалистичка Pепублика Босна и Херцеговина), commonly referred to as Socialist Bosnia or simply Bosnia, was one of the six constituent federal states forming the Socialist Federal Republic of Yugoslavia. It was a predecessor of the modern-day Bosnia and Herzegovina, existing between 1945 and 1992, under a number of different formal names, including Democratic Bosnia and Herzegovina (1943–1946) and People's Republic of Bosnia and Herzegovina (1946–1963).
Within Yugoslavia, Bosnia and Herzegovina was a unique federal state with no dominant ethnic group, as was the case in other constituent states, all of which were also nation states of Yugoslavia's South Slavic ethnic groups. It was administered under strict terms of sanctioned consociationalism, known locally as "ethnic key" or "national key" (Serbo-Croatian: etnički/nacionalni ključ), based on the balance of political representation of 3 largest ethnic groups (Bosnian Muslims, Croats and Serbs).