Poland is a democracy, with a president as a head of state, whose current constitution dates from 1997. The government structure centers on the Council of Ministers, led by a prime minister. The president appoints the cabinet according to the proposals of the prime minister, typically from the majority coalition in the Sejm. The president is elected by popular vote every five years. The current president is Bronisław Komorowski. The current prime minister, Donald Tusk, was appointed in 2007 after his party made significant gains in that year's parliamentary elections.
Polish voters elect a bicameral parliament consisting of a 460-member lower house (Sejm) and a 100-member Senate (Senat). The Sejm is elected under proportional representation according to the d'Hondt method, a method similar to that used in many parliamentary political systems. The Senat, on the other hand, is elected under a rare plurality bloc voting method where several candidates with the highest support are elected from each constituency.
With the exception of ethnic minority parties, only candidates of political parties receiving at least 5% of the total national vote can enter the Sejm. When sitting in joint session, members of the Sejm and Senat form the National Assembly (the Zgromadzenie Narodowe). The National Assembly is formed on three occasions: when a new President takes the oath of office; when an indictment against the President of the Republic is brought to the State Tribunal (Trybunał Stanu); and when a president's permanent incapacity to exercise his duties because of the state of his health is declared. To date only the first instance has occurred.