Sweden is a constitutional monarchy governed under the constitution of 1975, which replaced that of 1809. The hereditary monarch is the head of state but has little power. The prime minister, who is the head of government, is elected by the Parliament. Legislative power is vested in the unicameral Parliament or Riksdag, whose 349 members are elected by a system of proportional representation to four-year terms. The country's executive is the cabinet, headed by the prime minister, which must have the confidence of the Riksdag. Public administration is to a large extent decentralized, so that elected county and municipal governments play a major role in running the country. Administratively, Sweden is divided into 21 counties.