Here's a great article (in English) on today's race:
There are five main candidates, and voting may go to a second round on 12 February if no candidate wins more than 50% of the vote.
Q: How does the Portuguese political system work?
The January 2006 elections mark the end of Jorge Sampaio's presidency. Mr Sampaio, a Socialist, served the maximum of two five-year terms. The president is elected by universal suffrage and a candidate requires a minimum of 7,500 signatures to register his candidacy. Political parties may support a candidate but not field a candidate. To be elected, candidates need to obtain more than half of the valid votes cast. A second round, to be contested by the two candidates with the most votes, may be necessary.
Q: What does the president do?
The president's basic role is to represent the country, guarantee national independence and the state's unity as well as the normal functioning of institutions. The president is also the supreme commander of the Portuguese armed forces.
The president can dissolve parliament, dismiss the government, appoint the prime minister, call referendums, declare a state of siege or state of emergency, declare war and peace, approve and veto bills and decrees, and ratify international treaties.
Q: What happens on election day?
The election campaign ends two days before polling. Polling stations open on Sunday from 0800 to 1900 (0800 GMT to 1900 GMT).
Portuguese residing abroad may cast their vote two days prior to polling day, as well as on polling day itself. Results and exit polls may only be published after 1900 on polling day.
Q: Who are the main candidates?
Anibal Cavaco Silva
Born 1939. Joined Social Democratic Party in 1974. Prime Minister from 1985 to 1995. Stood for president against Jorge Sampaio in 1996, and returned to his post as professor of economics after losing.
Born 1957. Member of the Revolutionary Socialist Party since 1979, which is now part of the Left Bloc, founded in 1999. MP for Lisbon since 1999. Has published several political and economic books.
Jeronimo de Sousa
Born 1947. Joined Portuguese Communist Party in 1974. Elected PCP secretary-general 2004.
Born 1936. Joined Socialist Party in 1974. MP for Coimbra from 1974 to 2002 and for Lisbon since 2002. Deputy Speaker since 1995. He has won several literary prizes.
Born 1924. Exiled during Salazar's regime. Founder of Socialist Party and its secretary-general from the outset in 1973. Foreign minister in 1974-75. Prime minister 1976-78 and 1983-85. President 1986-1996.
Q: What are the main campaign pledges?
The president has more of a figurehead role and as such voters are choosing a personality rather than policies. The candidates' pledges are loosely based on those of the political parties which support them.
Anibal Cavaco Silva is the only centre-right candidate. Manuel Alegre is ahead of Mario Soares as the main candidate of the left. The latter's support comes mostly from his extensive political career including his 10 years as president.
All candidates have made general pledges such as to uphold the constitution, be the president of all the Portuguese and promote good institutional relations to ensure the normal functioning of democracy.
Anibal Cavaco Silva promises to contribute to putting the country on the road to development as well as bringing confidence and credibility.
Manuel Alegre says he is standing without party support but as a man of the Left. He vows to fight for a more just and prosperous society and to revive Portugal's political life.
Mario Soares promises to help the country overcome its "complex and prolonged" crisis and bring back a sense of pride to the Portuguese.
Q: Who is likely to win?
The latest poll published on 20 January suggests Anibal Cavaco Silva will be a clear winner in the first round with 53%. The scores for the other candidates were:
Manuel Alegre 20.6%
Mario Soares 12.4%
Jeronimo de Sousa 6.9%
Francisco Louca 6.1%
If these figures are reproduced on Sunday, then Mr Cavaco Silva would win outright without the need for a second round.