The Constitution of Estonia 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. The second Constitution was adopted on 24 January 1934, following a referendum in 1933, and was in force until the third Constitution was enacted on 1 January 1938. It remained in force, de facto, until 16 June 1940, when the Soviet Union occupied Estonia and, de jure, until 28 June 1992, when the fourth and current Constitution of the Republic of Estonia was adopted by referendum.
The first Constitution was a reflection of Jean-Jacques Rousseau's idea of national sovereignty. Power was split between the judiciary, the executive and the legislature according to the principles of Montesquieu. The Constitution provided for a high degree of public initiative and for referendums. Despite the Constitution being modelled upon Montesquieu's ideas, there was an imbalance, since the single-chamber Riigikogu exercised extensive power over the executive and the judiciary, leading to instability and frequent changes of government. The head of state and the head of government were combined in the post of State Elder.
Due to chronic government instability (18 governments headed by 10 State Elders), attempts were made to redraft the Constitution. In a referendum held in 1932, voters rejected two proposed drafts of a new Constitution, but a third draft, proposed by the populist Estonian War of Independence Veterans' League or Vaps Movement was adopted in a referendum in 1933 and came into force on 24 January 1934. This second Constitution vested broad powers in the head of state--still called the State Elder--while reducing the size and power of the Riigikogu. The State Elder had the power to issue decrees with the force of law. In order to prevent the Vaps Movement coming to power under this new Constitution, Konstantin Päts, who was serving as "Prime Minister in Duties of the State Elder" pending elections, seized power in a bloodless coup d’etat on 12 March 1934. He then suspended the Constitution and initiated the preparation of a third Constitution.