The 1955 State of Vietnam referendum determined the future form of government of the State of Vietnam, the nation that was to become the Republic of Vietnam. It was contested by Prime Minister Ngô Đình Diệm, who proposed a republic, and former emperor Bảo Đại, who had abdicated in 1945 and at the time of the referendum held the title of head of state.

Bảo Đại, born Nguyễn Phúc/Phước Vĩnh Thụy, was the 13th and final emperor of the Nguyễn dynasty, the last ruling dynasty of Vietnam. From 1926 to 1945, he was emperor of Annam and de jure monarch of Tonkin, which were then protectorates in French Indochina, covering the present-day central and northern Vietnam. Bảo Đại ascended the throne in 1932.