Iraq is a parliamentary democracy governed under a constitution that was ratified in 2005. The president, who is head of state, is elected by the Council of Representatives. The government is headed by the prime minister. The bicameral legislature consists of the 275-seat Council of Representatives, whose members are elected by proportional representation, and a Federation Council, whose membership had not been defined as of late 2007. Administratively, the country is divided into 18 governorates.