Egyptians are preparing to head to the polls in their first free presidential election, 15 months after ousting Hosni Mubarak in the Arab Spring uprising.
Fifty million people can vote, and security is likely to be tight.
The Supreme Council of the Armed Forces (Scaf), which assumed presidential powers in February 2011, has promised a fair poll followed by civilian rule.
The election pits Islamists against secularists, and revolutionaries against Mubarak-era ministers.
The frontrunners are:
- Ahmed Shafiq, a former commander of the air force and briefly prime minister during February 2011 protests
- Amr Moussa, who has served as foreign minister and head of the Arab League
- Mohammed Mursi, who heads Muslim Brotherhood's Freedom and Justice Party
- Abdul Moneim Aboul Fotouh, an independent Islamist candidate
Mr Mursi was originally the party's reserve candidate, but he was thrust into the limelight after its first choice, Khairat al-Shater, was disqualified by the Higher Presidential Electoral Commission (HPEC) over an unresolved conviction.
The Brotherhood have nevertheless likened Mr Mursi, a US-educated engineer and MP, to an underrated football substitute.
"In any match there is the reserve who plays in the last 10 minutes, scores the goal and wins the match. Mursi is our reserve player," said cleric Mohamed Abdel Maqsoud while addressing a crowd of Brotherhood supporters on Sunday.
A run-off vote is scheduled for 16 and 17 June if there is no outright winner.
BBC Middle East editor Jeremy Bowen says there is also a potential clash waiting to happen with the military, which seems determined to retain its position as the power behind the president's chair.
And the electorate does not know what powers the new president will have to do his job, as they are still waiting for them to be spelled out in a new constitution, our correspondent adds.
The election is being hailed as a landmark for Egyptians, who have the opportunity to choose their leader for the first time in the country's 5,000-year recorded history.
The Scaf, worried about potential post-election unrest, has sought to reassure Egyptians that it will be the voters themselves to decide the next president.
"It is important that we all accept the election results, which will reflect the free choice of the Egyptian people, bearing in mind that Egypt's democratic process is taking its first step and we all must contribute to its success," it said in a statement on Monday.
Prime Minister Kamal al-Ganzuri on Tuesday expressed hope that the election would be calm.
He called on "candidates, political forces, parties to urge their supporters to respect the will of others and accept the results of the election".
The 15 months since Mr Mubarak was forced from power has been turbulent, with continued violent protests and a deteriorating economy.
Foreign direct investment has reversed from $6.4bn (£4bn) flowing into the country in 2010 to $500m leaving it last year.
Tourism, a major revenue generator for the country, has also dropped by a third.
The new president will also have to reform the police to deal with the rash of crime that followed the uprising.
As many as a third of voters are reported to be undecided about which candidate to choose.
"I can't decide. I want someone who can provide stability and prosperity," Hussam Sobeih, 45, told the Reuters news agency.
"I was with the revolution until Mubarak was toppled but after that the situation worsened and I want to get my life back."
The Arab Spring began in Tunisia last year when weeks of protests forced President Zine al-Abidine Ben Ali from power, inspiring pro-democracy activists across the Arab world.
Egyptian President Hosni Mubarak, in power for three decades, resigned on 11 February 2011 after 18 days of protests in Cairo and other cities.