Israelis have taken part in parliamentary elections for the first time since 1999. BBC Middle East analyst Louisa Brooke looks at how the voting system works and how it is changing this time.

The Knesset

This election has its own peculiar challenge for Israelis - it's the second major change in the electoral system in less than a decade. After a brief experimentation with holding two separate elections for the parliament and the prime minister, Israel is reverting to its old system of one vote for one party.

No party ever wins a majority in the Knesset

Israel uses a system of proportional representation to elect political parties to the parliament, called the Knesset.

Seats in the Knesset are allocated in direct proportion to the number of votes a party or party bloc receives.

The system encourages a large number of parties because a party only needs to win 1.5% of the vote to gain a Knesset seat.

As the votes are split proportionally, no party ever wins enough of the 120 seats to command a majority, which means every government is a coalition of at least two parties. This gives the smaller parties considerable power to make or break a coalition government.

New system

To try to combat the exaggerated power of the smaller parties, Israel introduced a separate, direct election for the prime minister. The new system was meant to strengthen the prime minister and dilute the power of smaller parties.

However, it had the opposite effect when it was first used in 1996. The two largest parties, Likud and Labour, saw their support fall and several medium-sized parties grew in strength.

The system encourages a large number of parties

It also created the slightly awkward situation of a Likud Prime Minister, Binyamin Netanyahu, heading the government even though his party was only the second largest in the Knesset.

The new system also allowed elections for the prime minister and the Knesset to be held separately.

In February 2001, Israelis voted simply to change their prime minister rather than the entire parliament, which again saw a Likud Prime Minister, this time Ariel Sharon, lead a government with his party trailing Labour in the Knesset.

Party vote

The separate election system has now been dumped, and on 28 January Israel reverts to its original system. Unlike in other democratic countries, Israelis vote for a party rather than a candidate.

The party provides a "list" of its candidates and they are given Knesset seats depending on the number of votes they receive.

The parties use different methods to choose their candidates, and the higher up the list a candidate is, the more likely he or she will be elected to the new parliament.

To increase their chances of winning seats, parties often form factions or blocs to contest the election. Once in the Knesset these factions can then divide back into their natural parties and shift allegiances.

Coalition politics

No party ever wins a simple majority in the Knesset so after the election the Israeli President asks the leader of the party in the Knesset that has the best chance of forming a government. This is usually the largest party but if the vote is very close the decision of the president could be dramatic.

That person then has 28 days to put a coalition together.

The coalition must have a minimum of 61 members of the 120-member Knesset to govern, although any prime minister will endeavour to gather the support of as many members as possible to give it a large mandate.

Power of small parties

One of the side-effects of the system is the expansion of small and medium sized parties. Two parties have historically dominated political life: Likud, which is led by Ariel Sharon and on the centre-right of the political spectrum, and Labour, led by Amram Mitzna and on the centre-left.

On both sides lie a multitude of parties which describe themselves in a variety of ways. For example, Shinui describes itself as a centre, secular party, whereas the National Religious Party champions the settler movement.

In a coalition the power of the smaller parties is magnified and they can bring down governments if they dislike the decisions it is making.

The last three governments of Ariel Sharon, Ehud Barak and Binyamin Netanyahu were all brought to an early end because their coalitions fractured.

A coalition can include any number of parties. Ariel Sharon started his government in February 2001 with seven parties from across the entire political spectrum.

Broadly speaking, parties can be divided into left, centre and right, and divided again between the religious and secular.

Whoever wins the election will inevitably have to include at least some of these parties to form a viable coalition government.