Ehud Olmert, 60, (Kadima)
A career politician, Mr Olmert slipped seamlessly into the role of Israel's leader when Prime Minister Ariel Sharon suffered a massive stroke on January 4. Mr Olmert vowed to continue pursuing the former general's policy of breaking from conflict with the Palestinians, advocating unilateral withdrawal from isolated settlements in the occupied West Bank if peacemaking with the Palestinians remained frozen.
His lack of military experience has not hurt his electoral chances, while the seizure of a Palestinian militant leader from a West Bank jail this month boosted his security credentials.
Mr Olmert joined Mr Sharon's government in 2003 after a decade as the mayor of Jerusalem. As Mr Sharon's deputy, he gained a reputation for floating ideas widely seen as trial balloons for the prime minister.
He quickly followed Mr Sharon out of the right-wing Likud after the prime minister bolted to found the centrist Kadima party in November.
Amir Peretz, 54, (Labour)
A passionate socialist, the Moroccan-born Mr Peretz has struggled to focus the election campaign on fighting poverty and raising minimum wages. Many voters have expressed concern at the former trade union chief's lack of experience in government and military affairs, questioning how he would handle a security crisis.
Mr Peretz headed the Histadrut Trade Unions Federation until he upset elder statesmen Shimon Peres in a leadership vote for the Labour Party last November.
Sporting a bushy moustache, Amir Peretz has portrayed himself as a populist candidate who could help Labour shed its image as an elitist party for Israelis of European descent.
Benjamin Netanyahu, 56, (Likud)
A suave former prime minister and hawk on security, Mr Netanyahu had to try to pick up the pieces in the Likud he now heads after Mr Sharon left the party in the face of a far-right revolt among its members over Israel's Gaza pullout last year.
Known by his boyhood nickname "Bibi", Mr Netanyahu has won plaudits from the business community in Israel and abroad for his free-market policies as finance minister in Mr Sharon's government.
But he also has faced criticism over deepening poverty in the Jewish state.
Mr Netanyahu resigned the post last August in protest at the Gaza withdrawal. He opposes further unilateral "disengagements" and says his policy towards peacemaking with the Palestinians is based on reciprocity, often intoning: "If they give, they get. If they don't give, they don't get."
Avigdor Lieberman, 47, (Yisrael Beitenu)
An ultranationalist former cabinet minister, Mr Lieberman has been one of the surprises of the campaign. Opinion polls show his Yisrael Beitenu party winning around 10 seats in the 120-member parliament, only marginally fewer than Likud.
Mr Lieberman supports a Palestinian state but advocates ceding Israeli-Arab villages located adjacent to the West Bank for settlement blocs, a policy popular among right-wing voters but which Israeli-Arabs see as tantamount to ethnic cleansing.
Popular especially among Russian speakers, the Moldovan-born Mr Lieberman also has run a catchy slogan: "Olmert: Nyet, Netanyahu: Nyet, Lieberman: Da" ("Olmert: No, Netanyahu: No, Lieberman: Yes").