Riigikogu

23 April 1919, the opening session of the Estonian Constituent Assembly is considered the founding date of the Parliament of Estonia.[2] Established under the 1920 constitution, the Riigikogu had 100 members elected for a three-year term on the basis of proportional representation. Elections were fixed for the first Sunday in May of the third year of parliament.[3] The first elections to the Riigikogu took place in 1920. From 1923 to 1932, there were four more elections to the Riigikogu. The elections were on a regional basis, without any threshold in the first two elections, but from 1926 a moderate threshold (2%) was used. The sessions of the Riigikogu take place in the Toompea Castle, where a new building in an unusual Expressionist style was erected in the former courtyard of the medieval castle in 1920–1922.

In 1933 amendments to the first Constitution was approved by referendum, where more power was given to an executive President. The following year, the President used these new powers to adjourn parliament and declared martial law to avert an alleged coup.[4] In 1937, a second constitution was approved by referendum which saw the introduction of a two chambered legislature, the Chamber of Deputies (Riigivolikogu) and the National Council (Riiginõukogu). Elections were subsequently held in 1938 where only individual candidates were allowed to run.

During the subsequent periods of Soviet occupation (1940–41), German occupation (1941–44), and the second Soviet occupation (1944–1991) the Parliament was disbanded. The premises of the Riigikogu were used by the Supreme Soviet of the Estonian SSR during the second Soviet occupation.

In September 1992, a year after Estonia had regained its independence from the Soviet Union, elections to the Parliament took place on the basis of the third Constitution of Estonia adopted in a referendum in the summer of the same year. The 1992 constitution, which incorporates elements of the 1920 and 1938 Constitutions and explicitly asserts its continuity with the Estonian state as it existed between 1918 and 1940, sees the return of a unicameral parliament with 101 members. The most recent parliamentary elections were held on 5 March 2023. The main differences between the current system and a pure political representation, or proportional representation, system are the established 5% national threshold, and the use of a modified D'Hondt formula (the divisor is raised to the power 0.9). This modification makes for more disproportionality than does the usual form of the formula.