Recent opinion polls suggest Mr Ortega is leading with 31%
Nicaraguans vote on Sunday for a new president, vice-president and National Assembly.
Former President Daniel Ortega is ahead in the polls, but analysts say he could face a tight race if a second round of voting in the presidential poll is required on 20 December.
Who are the leading candidates?
Daniel Ortega led the country from 1979 - when his left-wing Sandinista National Liberation Front deposed the military ruler, Anastacio Somoza - until 1990. During his time in office (he was elected president in 1984) he resisted the US-backed Contra rebels.
The Sandinista leader has since been defeated in three consecutive presidential elections. This time around he is pledging to respect private banking laws and land ownership, while supporting small farmers and miners in a bid to tackle unemployment, illiteracy and hunger.
His running mate, Jaime Rene Morales Carazo, is a former Contra spokesman who has helped modify the former president's image.
Conservative candidate Eduardo Montealegre Rivas is backed by the outgoing government and is also promising support for farmers and small businesses. He hopes to reduce emigration by creating jobs at home, but also favours voting rights for Nicaraguans living abroad.
He supports the Central America Free Trade Agreement (Cafta) with the US and has labelled it the "the best free-trade agreement we could hope for".
Running for the Nicaraguan Liberal Alliance-Conservative Party (ALN-PC), Mr Montealegre is an experienced politician and has an MBA from Harvard University in the US.
And the others?
A further three candidates are taking part in the presidential race.
Running for the Constitutionalist Liberal Party (PLC), former vice-president Jose Rizo has called for stockpiling energy and for promoting employment and access to health care.
Mr Rizo favours rural development, including the decentralisation of power to municipalities. His running mate Jose Antonio Alvarado heads the Liberal Democratic Party and was an unsuccessful vice presidential candidate in the previous election.
Former diplomat and legislator Edmundo Jarquin Calderon has pledged to promote government reform and to crack down on corruption. He wants to impose a single-term limit on the presidency. A professor at the University of Central America, he has a legal and social sciences background.
Eden Atanacio Pastora Gomez participated in the guerrilla campaign in the 1970s against the dictatorship of Anastacio Somoza. Running for the Alternative for Change (AC), Mr Pastora has called for improvements in education, environmental protection and more development aid to Nicaragua's autonomous regions.
His vice-presidential candidate Mercedes del Socorro Tenorio, a nurse and mother of four, is the only female candidate in the race.
What are the main issues?
Nicaragua is the second-poorest country in the Americas. With an economy largely based on the export of cash crops, such as coffee and bananas, more jobs and improved health and education are central to most of the candidates' campaigns.
The Cafta, which Nicaragua ratified in 2005, is still a topic of active debate in the run-up to the elections.
Mr Ortega's ties with Venezuelan President Hugo Chavez have been an issue throughout the campaign. Although he has not openly addressed the topic, his opponents have criticised what they see as Caracas's intervention in the country's domestic affairs.
What do opinion polls indicate?
Mr Montealegre is promising support for farmers
Recent opinion polls suggest Mr Ortega may fall short of the 40% of votes needed for an outright victory, giving him about 31%, followed by Mr Montealegre at 26%.
However, under a constitutional change pushed through by the Sandinistas six years ago, a candidate could avoid the second round by winning just 35% of the initial vote provided he finishes at least 5% ahead of his closest rival.
The polls put Mr Rizo third with 14%, while 10% of voters have said they support Mr Jarquin.
How does the National Assembly election work?
Sunday's vote will fill 90 of the 92 seats in the National Assembly. Out of these, 20 are distributed to the political parties. A further 70 seats are allocated to 15 departments and two autonomous regions.
The remaining two seats are filled by the outgoing president and the runner-up in the current elections.
Who can vote?
Some 3.4 million people are registered to vote at the country's 11,200 polling stations. Nicaraguans living abroad are not eligible to participate.
Are the polls expected to be free and fair?
The elections are being watched by 16,000 local and 1,000 foreign observers. More than 8,000 soldiers will be stationed around the country to keep the peace.
Foreign Minister Oscar Garcia has said that while "fraud is not impossible", it is unlikely because of the "many safeguards" put in place.
The new president will be inaugurated on 10 January 2007.
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