President Susilo Bambang Yudhoyono is favoured to keep his job
Indonesian President Susilo Bambang Yudhoyono is looking to secure a second term in office as campaigning for the 8 July vote officially opened.
Opinion polls indicate he is the favourite after his Democratic Party nearly tripled its share of the vote in April's parliamentary elections.
Competition is led by former president Megawati Sukarnoputri and former vice-president Jusuf Kalla.
Officials said they were confident of a fair and peaceful vote.
Democracy was only established in Indonesia after the fall of Suharto's military-backed rule in 1998.
Mr Yudhoyono has said he wants a second term to fulfil his promises to clean up corruption and secure economic growth amid the world recession.
A former general, he has ditched his former vice-presidential partner, Jusuf Kalla of the old-established Golkar Party, in favour of the former central bank chief, Boediono (who uses only one name).
Ms Megawati was defeated by Mr Yudhoyono in the 2004 elections, which were the first to produce the country's head of state by direct elections.
Mr Kalla's decision to run separately for president complicates the race, which will go to a second round in September if no clear winner emerges.
Former generals feature in each of the three leading presidential tickets.
Ms Megawati has teamed up with the notorious special forces ex-commander Prabowo Subianto, who is accused of serious human rights violations, including the kidnapping of activists on behalf of the Suharto regime in the 1990s.
Mr Kalla has chosen former military chief Wiranto as his running mate.
Mr Wiranto was indicted by the United Nations for crimes against humanity including murder, deportation and persecution over East Timor's bloody independence referendum in 1999.
Indonesia has about 176 million voters.