Yala maintains that he remains head of state
Voters in Guinea-Bissau go to the polls on Sunday in the first round of a presidential election as part of a plan to return the country to democracy. The previous incumbent was overthrown in a bloodless coup in September 2003.
What is at stake?
The poll is attracting controversy because the ousted president, Kumba Yala, and his predecessor, Joao Bernardo "Nino" Vieira, are staging a comeback.
Both were barred from standing under a transitional agreement which, shortly after the coup, ushered in a new civilian administration headed by interim President Henrique Rosa.
The Supreme Court overturned legal obstacles to their candidacies in early April, on grounds which to many remain unclear.
Mr Yala had said that if the Supreme Court did not allow him to run, he would seize power himself. He also says he still regards himself as the legal head of state.
What happened in the last presidential race?
In the November 1999, none of the 12 candidates got through in round one, so it went to a run-off in January 2000.
In that contest Mr Yala, representing the Social Renewal Party (PRS), got 72% of the vote.
His rival Malam Bacai Sanha, of the African Party for the Independence of Guinea and Cape Verde (PAIGC), won just 28%.
But the PAIGC won parliamentary elections in March 2004. These elections, like the current poll, were part of the transitional arrangement for a return to constitutional order.
What are the president's powers?
The president is elected for five years and may serve no more than two terms.
The constitution says the president is head of state, supreme commander of the armed forces, symbol of national unity, as well as guarantor of national independence and the constitution.
The president has the right to dissolve the National Popular Assembly, or parliament, at times of political crisis.
He appoints the prime minister in line with party representation in parliament. The prime minister heads the government.
The National Popular Assembly passes laws and can also revise the constitution.
Who are the main candidates?
Kumba Yala, a former philosophy teacher, won the presidency in 2000 on a platform of national reconciliation, following a bitter civil war in the late 1990s in which thousands were killed, wounded or displaced.
Known for his nationalism and fiery speeches, he was initially popular, especially among jobless urban youths. He was overthrown after his government dismissed parliament and failed to call new elections.
In March 2005 he was adopted as presidential candidate by the Social Renewal Party (PRS), the largest opposition party in parliament.
It commands strong support from the Balanta, Guinea-Bissau's largest ethnic group, which is heavily represented in the army and to which Mr Yala belongs.
Joao Bernando "Nino" Vieira, another former president, is a former army general who seized power in a military coup in 1980.
He ruled for almost 19 years until he was forced out in a coup in 1999. He returned to the country in April after six years of exile in Portugal.
He is running as an independent. However, several influential leaders within the ruling African Party for the Independence of Guinea-Bissau and Cape Verde (PAIGC) have reportedly backed his bid.
Malam Bacai Sanha served as interim vice-president between 1999 and 2000. He is the official candidate of the PAIGC.
Mr Sanha came a poor second to Mr Yala in 2000, even though it was the PAIGC which won the 2004 parliamentary election.
PAIGC was the party which launched the 1963-1974 war of independence from Portugal and then established a one-party state.
In May, the PAIGC Central Committee suspended 37 party members, including party vice-president Aristides Gomes, after they publicly backed the candidacy of Joao Bernando Vieira.
Will there be observers?
The EU has said it is deploying 90 observers around the country to monitor the poll.
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