Israel’s government is a parliamentary democracy. The Israeli political system has three branches: executive, legislative and judicial. The legislative branch is comprised of the Knesset, Israel’s parliament, which has 120 members.
The two largest parties historically were the Likud party, which is a center-right party, and the Labor party, which is a center-left party. In 2005, Ariel Sharon founded the Kadima party in order to support his disengagement plan. Moderate Likud and like-minded Labor politicians joined the party, and Kadima won the majority of seats in the Knesset in both the 2006 and 2009 elections.
There are also several "religious" parties ranging in ideology from modern Orthodox to ultra-Orthodox, and a secularist party, Shinui, which also claims to be the party of the "middle class." In addition, there are several Arab parties, and a communist Arab-Jewish party. It should be noted that although parties are considered "Arab" or "Jewish," this does not mean that Arabs are not members and even elected representatives of different Jewish Israeli parties--they are. The Labor, Likud, and Kadima parties all count among their delegates Arab-Israeli citizens.
Smaller parties (including religious parties) are also important in Israeli politics, as their support is necessary to form a coalition required to pass legislation. Small parties can represent identity groups--such as Sephardim (Jews of Mediterranean, Middle Eastern, or Spanish descent), secular Israelis, or immigrants--or they can be formed to advocate for a single issue, such as environmental-protection legislation.
The executive branch of Israel is headed by a prime minister who is the coalition leader of the Knesset. In an election, voters vote for party lists rather than individual candidates, with seats in the Knesset apportioned according to the percentage of votes each party receives in the election. After the election, a coalition government must be formed of the elected party representatives in the Knesset; a ruling coalition must have at least 61 members to ensure a majority of the 120 seats.
The president of Israel formally asks whichever party leader he or she feels is most likely to be successful in forming a government to attempt to do just that and piece together a majority coalition. But since no party has ever achieved a 61-vote majority on its own, they have always relied on other parties to join the coalition; this has given small parties--some with as few as a single Knesset representative--power and importance that they otherwise would lack in the government, with parties agreeing to join a coalition in return for the passage of their pet bills.