Favourite to win the election is acting president Rupiah Banda
Voters in Zambia head for the polls on 30 October to elect a new president to succeed Levy Mwanawasa, who died on 19 August after suffering a stroke in June.
Mr Mwanawasa was voted into power in 2006. The winner of the 2008 by-election will serve out the remainder of the late president's term, which was due to end in 2011.
How will the president be elected?
The constitution stipulates that by-elections must be held within 90 days of the death of a sitting president.
Due to time constraints, there was no fresh voter registration exercise this year so the 2006 voter's register is being used for the by-election.
According to the electoral commission, 3.9 million Zambians are registered to vote. They will cast ballots for their favourite candidate at the 6,240 polling stations countrywide.
The candidate with the majority of votes will be declared president. The results are expected to be announced between 3 and 9 November.
Who are the candidates?
There are four presidential candidates. Rupiah Banda is acting president. He is facing rivals Michael Sata, Hakainde Hichilema and Godfrey Miyanda - all of whom stood against Levy Mwanawasa in 2006.
Rupiah Bwezani Banda
Mr Banda, 70, beat 19 aspirants for the nomination of the ruling Movement for Multiparty Democracy (MMD). As deputy president, he was a close ally of Mr Mwanawasa.
Mr Banda has widespread support among tribal leaders in eastern Zambia, a stronghold for the ruling party.
A career diplomat, he served as ambassador to the US and permanent representative at the UN before becoming foreign minister in 1975.
Three opposition parties, the Federal Democratic Party (Fedepa), the United Liberal Party (ULP) and the New Generation Party (NGP) have pledged to support him and are not fielding candidates for the by-election.
Michael Chilufya Sata
Michael Sata founded the opposition Patriotic Front (PF) party in 2001 after having fallen out with his close partner, former President Frederick Chiluba of the ruling MMD. Mr Sata has served at different times as minister for local government, labour and health.
He came second to Mr Mwanawasa in the 2006 presidential election winning 29% of the vote, despite reports of "a commanding lead" ahead of the count. He maintains the last election was stolen from him.
Hakainde Hichilema, a wealthy businessman, is the candidate for the United Party for National Development (UPND). He ran in the 2006 presidential election as the head of the United Democratic Alliance (UDA) and came third. Mr Hichilema enjoys overwhelming support in Southern Province, his home region.
Godfrey Miyanda of the Heritage Party was dismissed from the army in 1990 by first President Kenneth Kaunda for involvement in an alleged coup plot. Between 1993 and 1997 he served as vice-president in the government of President Chiluba, who succeeded Mr Kaunda. He subsequently served as education minister, minister without portfolio and national secretary still under President Chiluba. He too, took part in the 2006 election.
What are the main issues?
Levy Mwanawasa's legacy
Mr Mwanawasa was a widely respected African statesman. At home, he initiated an anti-corruption campaign and even stripped his predecessor and former mentor, Fredrick Chiluba, of immunity so he could face charges of corruption. In the region, he was known as one of the few early vocal critics of Robert Mugabe, president of neighbouring Zimbabwe. As chairman of the regional political body, the Southern African Development Community (SADC), he criticised Zimbabwe's flawed presidential elections in 2008.
Acting President Rupiah Banda on the other hand has been quoted as saying that Robert Mugabe showed courage when he embarked on his controversial land reform programme in the face of Western criticism.
Mr Banda's main rival, Michael Sata, says he wants to continue Levy Mwanawasa's fight against corruption and "reinvigorate" institutions of accountability such as the Auditor-General's Office and the Anti-Corruption Commission.
Almost 30 years of socialism under Kenneth Kaunda, followed by an era of privatisation marked by corruption under Fredrick Chiluba, left an ailing economy in Zambia. The country is one of the poorest in the world. The late Levy Mwanawasa sought to kick-start the economy with pro-market policies, which Rupiah Banda has vowed to continue.
Presidential candidate Michael Sata, meanwhile, famously criticised foreign business owners in his populist 2006 campaign. He threatened to deport Chinese, Indians and Lebanese, who he accused of mistreating Zambian workers. He has this time round toned down his attacks on foreign businessmen.
Hakainde Hichilema has promised that if elected, Zambia's children will receive free primary and secondary school education as part of a drive to reduce poverty.
Will there be foreign observers?
A network of non-government organisations (NGOs) is deploying 6,456 monitors at polling stations throughout Zambia. They include members of the Anti-Voter Apathy (Avap), Forum for Democratic Process (Fodep), Zambia National Women's Lobby Group (ZNWLG) and the Southern African Centre for the Constructive Resolution of Disputes (Saccord).
International observers, including representatives of the African Union, the United Nations will also be monitoring the polls.
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