Israel is a democratic republic, with no written constitution. Legislative power is vested in the unicameral Knesset (parliament), whose 120 members are elected for four-year terms by universal secret vote of all citizens 18 years of age and over, under a system of proportional representation. New elections may be called ahead of schedule, and must be held when the government loses the confidence of a majority of parliament.
The head of state is the president, elected by the Knesset for a five-year term. The president performs largely ceremonial duties and traditionally choses the prime minister from the ruling political party. In 1996, however, a new law went into effect whereby the prime minister would be directly elected by the people. In May of that year, Benjamin Netanyahu became Israel's first directly elected prime minister. Three years later he was succeeded in that post by Ehud Barak. In March 2001, the Knesset voted to change the system of direct elections and restore the one-vote parliamentary system of government that operated until 1996. The law went into effect with the January 2003 elections, won by Likud. The cabinet, headed by the prime minister, is collectively responsible to the Knesset, whose confidence it must enjoy.