South African troops have been helping to secure the polls
Comorans go to the polls on 14 May for the second round of a presidential election which observers see as a key test of whether the Indian Ocean archipelago can make the transition to peaceful political change following three decades of instability.
Who are the candidates?
Three candidates remain from the 13 contenders who stood in last month's first round of voting.
Ahmed Abdallah Mohamed Sambi, an Islamic preacher and former MP, popularly known as "the Ayatollah"; he is also a founding member of the Islamic National Front for Justice party.
Mr Sambi has promised to end corruption, create employment and build housing. He studied politics and Islam in Saudi Arabia, Sudan and Iran. His candidacy has generated a debate over the role of religion in the country.
Mr Sambi owns a radio station (Radio Ulezi) and a TV station (TV Ulezi). He won the first round, taking nearly 24% of the votes.
Mohamed Djanffari, the current vice-president of the federal National Assembly. A former member of the French air force, he has extensive interests in the country's transport sector and has focused his campaign mostly on his native island of Anjouan.
Mr Djanffari took 13% of the first round votes, coming second.
Abderemane Ibrahim Halidi, a former prime minister and teacher from the deprived region of Nioumakele in Anjouan; he is being supported by the incumbent president and his party, the Convention for the Restoration of Comoros but is a member of the Movement for the Comoros Party (MPC).
He has pledged to stick to the current government's development plan. He polled more than 10% of first round votes.
What's at stake?
Since independence from France in 1975, the country has witnessed some 19 coup attempts - four of them successful - often involving foreign mercenaries, as well as bitter inter-island strife and assassinations.
Western observers have described the polls as a turning point, with a successful election being seen as a test of Comoros' power-sharing arrangements and its quest to end its image as a chronically unstable country.
The people of the Comoros are among the poorest in Africa and are heavily dependent on foreign aid.
Concerns have been expressed that if the international community does not consider the polls to be largely free and fair, it could delay the disbursement of aid worth some $200 million pledged as part of a three-year development plan in 2005.
What's the political system?
Under the constitution and political agreements reached in 2001, the Union presidency rotates every four years between Comoros' three semi-autonomous islands - Grande Comore, Anjouan and Moheli.
President Azali Assoumani, from Grand Comore, won the first election in 2002 after coming to power via a bloodless coup three years earlier. In mid-2005, he tried unsuccessfully to change the rules and stand for a second term but is ineligible to run.
It is now Anjouan's turn to hold the presidency. On 16 April its voters short-listed three candidates for the second round on 14 May, in which voters from among the population of all 670,000 Comorans will vote.
The union president has two deputies who must not come from the same island as the president.
Are there any observers?
The first round voting was peaceful, although there were some allegations of ballot fraud, as well as delays at some polling stations.
The results were initially delayed by the constitutional court - the highest electoral body - over contested results but were judged to have been free and fair.
The elections are being carefully scrutinised by Comoros' neighbours, in particular South Africa, as well as by the African Union (AU) and Arab League.
South Africa is leading a 460-strong AU mission which began operations in the capital Moroni at the end of March. It is sending additional troops to help secure the second round of polls.
One of the mission's key aims is to ensure that Comoran troops do not interfere in the voting. On 9 May, the AU issued an explicit warning to the Comoran security forces not to disrupt the polls.
The warning followed recent attacks on two radio stations on Grand Comore, and the closure by the local authorities of Radio Moheli.
BBC Monitoring selects and translates news from radio, television, press, news agencies and the internet from 150 countries in more than 70 languages. It is based in Caversham, UK, and has several bureaux abroad.