The Alþingi (anglicised as Althingi or Althing) is the national parliament of Iceland. It is the oldest parliament in the world. The Althing was founded in 930 at Þingvellir ("thing fields"), situated approximately 45 kilometres (28 mi) east of what later became the country's capital, Reykjavík. Even after Iceland's union with Norway in 1262, the Althing still held its sessions at Þingvellir until 1800, when it was discontinued for 45 years. It was restored in 1844 and moved to Reykjavík, where it has resided ever since. The present parliament building, the Alþingishús, was built in 1881, of hewn Icelandic stone.

The unicameral parliament has 63 members, and is elected every four years based on Party-list proportional representation.

The constitution of Iceland provides for six electoral constituencies with the possibility of an increase to seven. The constituency boundaries and the number of seats allocated to each constituency are fixed by legislation. No constituency can be represented by fewer than six seats. Furthermore, each party with more than 5% of the national vote is allocated seats based on its proportion of the national vote in order that the number of members in parliament for each political party should be more or less proportional to its overall electoral support.

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