The Finnish electoral system was introduced in 1906. Elections were held the following year, which were the first free proportional elections for both men and women. In 1917 Finland became independent from Russia, and the founding Constitution of the new Republic was put into force in 1919; later a variant of parliamentarism known as semi-presidentialism was developed. Since 1906, all women and men have been eligible to vote and to be nominated in elections. The age of eligibility has been successively lowered from 24 in 1906 to 21 in 1944, to 20 in 1969 and to 18 in 1972. One distinctive feature of Finnish elections is the exceptionally high numbers of ballots cast in absentia by post. At the 1995 election, 43.4 percent of the valid votes were so cast.

The Finnish parliament consists of 200 MPs elected from 15 districts. In all districts, except on the Swedish-speaking land Islands, the allocation of seats to parties (including electoral alliances) is proportional to the votes following a d'Hondt system of party list Proportional Representation, see Mixed Member Proportional. Before 1954, voters had to choose between candidate lists (a list included a maximum of two candidates and one alternate); later changes to the system mean that it is now possible to vote for one individual candidate only. This change transformed the Finnish electoral system into a rare type of list system, which obliges voting for individual candidates.

The election of candidates from the party list is not predetermined, but depends entirely on the number of individual votes cast for each candidate. The voter picks the allotted number of his or her candidate (the list of candidates, each with an identifying number, hangs in front of the voter) and writes it down on the ballot. As a result, the election is not exclusively a competition between parties; it is also a competition between single candidates on the party list. Neither is the electorate given the option to vote for a party per se; but only for individual candidates nominated, but not ranked by a party or a non-party list. While the Aland Islands district elects a single member, the other 14 districts are all multi-member. The district magnitude is determined by the population size, which favours the constituencies in the rural north and east. Proportionality is still high in overall parliamentary results, although variation between constituencies in this respect is large. In general, urbanised constituencies are more proportional, and more rural areas produce more disproportional results.