The Constitution of Estonia (Estonian: Eesti Vabariigi põhiseadus) is the fundamental law of the Republic of Estonia and establishes the state order as that of a democratic republic where the supreme power is vested in its citizens. The first Constitution was adopted by the freely elected Estonian Constituent Assembly on 15 June 1920 and came into force on 21 December 1920.[1] Heavily amended[2] on 24 January 1934, following a referendum in 1933, it was in force until the second Constitution was enacted on 1 January 1938.[3] It remained in force, de facto, until 16 June 1940, when the Soviet Union occupied Estonia and, de jure, until 28 June 1992,[4] when the third and current Constitution of the Republic of Estonia was adopted by referendum.[5]