[This post has been updated.]
Unlike in some other parliamentary democracies, Israelis don't vote for a specific geographic constituency: Rather, they vote for a slate of candidates represented by a party or coalition of parties. Here's a primer on the main parties vying for seats, and where their allegiances may fall in a future government.
The political alliance links together Herzog's Labor and the Hatnuah party of Tzipi Livni, most recently justice minister, who is an ardent supporter of a two-state solution for the Israelis and Palestinians. If victorious, the pair would rotate the post of prime minister in two-year terms.
The Zionist Union has surged in polls on the back of popular dissatisfaction with Netanyahu, fueled most keenly by Israel's many economic woes. Housing prices and the general cost of living rank among the most urgent concerns for Israeli voters -- something that's a problem for Netanyahu, the leader who some say created this mess. The latest voter surveys suggest Zionist Union could win 24 seats, or two to four more seats than Likud.
Herzog, a four-time former government minister, lawyer and a "scion of rabbinical, military and political aristocracy," as my colleagues put it, has emerged as the fulcrum of the Anybody-but-Netanyahu movement. "We are having a deep debate with Netanyahu and his Likud party because it's either we win or he stays on," Herzog told The Post's William Booth and Ruth Eglash.
The influential, right-wing party has campaigned primarily on Netanyahu's security agenda -- framing the choice for voters as one between a leader who will be tough on Iran and the threat of Islamist militants or a feckless, appeasenick opposition. Likud issued a number of controversial ads, including one showing Islamic State fighters infiltrating Israel should the country turn to the left.
But the prime minister's pronounced hawkishness, highlighted by a polarizing speech two weeks ago in Washington, has failed to arrest Herzog's lead. "Our security is at great risk because there is a real danger that we could lose this election," Netanyahu said in one of his last campaign rallies.
Some 20 percent of Israel's nearly 6 million eligible voters are Palestinian, also referred to as Israeli Arabs. For decades, Israel's Arab parties have been divided by all sorts of political differences: between right and left, secularists and Islamists. But a new law pushed through by Netanyahu's government, which raised the threshold of votes needed to win seats in the Knesset, threatened the survival of the Arab parties.
The united Arab bloc -- known as the Joint List -- may win more than a dozen seats in the Knesset, despite past Palestinian voter apathy and previous boycotts of elections. The Joint List has ruled out partnering in a government led by Herzog and would never consider Netanyahu. But Arab politicians could play an important role in supporting a Herzog government even if they remain in the official opposition.
Yesh Atid ("There Is a Future")
The centrist party is led by the telegenic ex-newscaster Yair Lapid, who served as finance minister in Netanyahu's ruling coalition until differences between the duo led to a falling out and spurred Netanyahu's calls for early elections. Yesh Atid, like other centrist, secularist parties, has campaigned on an agenda of domestic economic reform. Lapid has also been outspoken in his opposition in his call to "share the burden" by pushing ultra-Orthodox Jews here to work and serve in the army, rather than continue to enjoy welfare benefits and army deferrals.
Bayit Hayehudi ("Jewish Home")
The rise during previous elections of Jewish Home and its leader, tech millionaire Naftali Bennett, is symbolic of Israel's larger lurch toward the right in recent years. Overtly religious and staunchly opposed to a Palestinian sovereignty, Bennett is backed by a base of religious Zionists and the pro-settler camp. As economy minister in Netanyahu's government, Bennett worked against a two-state solution with the Palestinians. His party is projected to win at least 12 seats and would likely partner once more with Likud.
Kulanu ("All of Us")
Kulanu, another centrist faction, emerged last year as the project of Moshe Kahlon, a former Likud minister. Kahlon became popular with voters after he busted cellphone monopolies and prices of mobile minutes plummeted. His party's candidates include Michael Oren, former Israeli ambassador to the United States, who rebuked Netanyahu for addressing Congress two weeks ago. Kulanu is expected to win more than 10 seats, and its leader may emerge as the kingmaker who helps Netanyahu or Herzog form the next coalition government.
The party of ultra-Orthodox Sephardic Jews, Shas was the fifth-biggest party in the Knesset until it split apart in a fight over leadership. Its leader, the Moroccan-born Aryeh Deri, has already said his party will ally with a Likud-led coalition, but wants to see progress for poorer citizens, particularly those not of Ashkenazi descent. A Shas campaign video, below, poked fun at the complaints of Israel's more secular middle class.
United Torah Judaism
A party of Ashkenazi ultra-Orthodox Jews, the UTJ, like Shas, is a reflection of the growing electoral influence of Israel's ultra-Orthodox or "haredi" community on the country's politics -- driven both by immigration and the higher birth rates of the country's more devout communities. United Torah could join either a Netanyahu or Herzog coalition, dependning on who else sits in the government and what they are offered.
Yisrael Beitenu ("Israel Is Our Home")
Headed by current Israeli Foreign Minister Avigdor Lieberman, Yisrael Beitenu is an ultra-nationalist, secularist party that draws much of its support from immigrants from the former Soviet Union. As my colleagues William Booth and Ruth Eglash reported, Lieberman is in bad shape ahead of the elections, and that's not because of the strident anti-Arab rhetoric that earned him notoriety outside Israel. Instead, his party is suffering from the stigma of corruption scandals and the wariness of non-Russian-speaking Israeli voters. There's a small risk it may not even cross the threshold of votes needed to win a seat in the Knesset.
The difficulties facing Meretz, Israel's traditional secular-leftist party, are a sign of the larger plight of the diminished Israeli left. It's now urging voters who are considering casting their ballot for the Zionist Union to stick with them. "We must not lose Meretz," is a rather depressing new campaign slogan. It counts Jewish-American comedian Sarah Silverman as one of its supporters.