Serbian President Boris Tadic and hardline nationalist Tomislav Nikolic are rivals in a run-off presidential vote on 3 February that pollsters say is too close to call. Mr Nikolic narrowly won the first round.
The election comes at a sensitive time as Kosovo prepares to declare independence from Serbia.
BORIS TADIC (Democratic Party, DS)
Son of a communist-era dissident, 50-year-old Boris Tadic is a life-long political activist.
Mr Tadic has been running an aggressive campaign on Kosovo
He was convicted for his opposition activities while studying psychology in Belgrade in the then Yugoslavia.
In the mid-1990s he fought the nationalist regime of Slobodan Milosevic, whose rule was eventually ended in 2000.
He was telecommunications minister in the first post-Milosevic government.
Mr Tadic then quickly gained the reputation of being a leading pro-Western reformer, taking over from assassinated Prime Minister Zoran Djindjic as leader of the centre-left Democratic Party in 2004.
Later that year he managed to defeat Tomislav Nikolic in a presidential election run-off, despite losing in the first round.
He now hopes to repeat that feat, after again finishing second in the first round of the election on 20 January. He got 35.4%, while Mr Nikolic got 40%.
In the current campaign, he has been wooing voters with pledges to speed up Serbia's accession to the European Union, warning that Serbia risks isolation in Europe.
At the same time, he has been running an aggressive campaign on Kosovo, promising that he will never give up the southern province.
"I will never accept the independence of Kosovo... we will do everything for Kosovo to stay in Serbia," Mr Tadic said during a symbolic visit to Kosovo on the final day of campaigning.
The move is aimed at projecting him as a defender of Serbia's national interests and also at drawing votes from Mr Nikolic, analysts say.
Mr Tadic's election slogans are "For a strong and stable Serbia" and "Let us conquer Europe together".
However, his coalition partner, moderate nationalist Prime Minister Vojislav Kostunica, has refused to back him in the run-off.
Mr Tadic was born in the Bosnian capital Sarajevo in 1958. He is married and has two children.
TOMISLAV NIKOLIC (Serbian Radical Party, SRS)
Tomislav Nikolic, 55, has led the nationalist Serbian Radicals since February 2003. That was when party boss Vojislav Seselj gave himself up to the UN tribunal in The Hague, to face war crimes charges relating to the conflicts in the former Yugoslavia in the 1990s.
Mr Nikolic hopes to repeat his success in the first round
Demonised by the West as a spiritual successor to Slobodan Milosevic, Mr Nikolic has been trying to soften his rhetoric during the election campaign.
Although he has vowed never to give up Kosovo, he says the province should be defended by diplomatic means alone.
"Serbia will no longer send its children to war," he says.
Like Mr Tadic, Mr Nikolic also advocates Serbian membership of the EU, but not at all costs.
He says he prefers an "open" road towards Russia to a "thorny" path towards the EU. His statements that Serbia should be a Russian province have been quoted frequently in the local media.
"Russia is our friend, who will prevent the United States and European Union from taking Kosovo away from us," Mr Nikolic has said.
This is the fourth time he has run for the presidency since 2000. His election slogan in the current campaign is "Wholeheartedly for Serbia".
Mr Nikolic was one of the founders of the SR in 1991. He served as Yugoslav deputy prime minister in 1999, when the party formed a coalition with Slobodan Milosevic's Socialists.
In 2007, Mr Nikolic was elected Speaker of parliament, but was dismissed just five days later, amid an outcry over his appointment.
Mr Nikolic was born in Kragujevac in 1952 and later studied civil engineering. He is married and has two children.