Election day in Nigeria on 19 April is just part of a hectic period of voting, with four different polls in less than a month. Joseph Winter, who is in Nigeria for BBC News Online, explains what is at stake.
Why are these elections important?
Nigeria is by far the most populous country in Africa, with some 120 million people.
About 20% of all Africans are Nigerian. Nigeria is also the world's sixth largest oil producer.
Since the 11 September 2001 attacks, the United States has tried to reduce its reliance on Middle Eastern oil by buying more from African producers, including Nigeria.
For much of its history, Nigeria has been ruled by the military. It is hoped that these will be the first successful civilian-run elections for 20 years.
Which jobs are up for grabs?
On 12 April, Nigerians elected their next national assembly.
President Olusegun Obasanjo's ruling party secured an outright majority in both the 360-member lower house and the 109-member senate, but opposition parties alleged massive rigging.
On 19 April, as well as choosing their next president, Nigerians decide on the governors of Nigeria's 36 states.
Then, on 3 May, they will elect their state houses of assembly.
Who will win?
Most people expect President Obasanjo to be re-elected for a second term in office, especially after the ruling party's triumph on 12 April.
His main challenger is likely to be Muhammadu Buhari, a northern Muslim. Both men are former military rulers.
Some analysts had feared that an election between a southern Christian and a northern Muslim would ignite religious tensions in this volatile and diverse country, where several thousand people have been killed in communal clashes since the return of civilian rule in 1999.
Some of the worst violence has been over the reintroduction of Islamic Sharia law in the northern states.
Has there been any electoral trouble?
During the 12 April vote, about a dozen people died, but this was deemed to be not as bad as it could have been.
During the campaign, several politicians were assassinated, most notably Marshall Harry, one of the leaders of Mr Buhari's All Nigeria People's Party.
Most of the heat seems to be coming from the elections for state governors, as many people see Mr Obasanjo's re-election as a foregone conclusion.
State governors have considerable powers in this federal state and these are plum jobs.
Some 260,000 security agents will be out during the elections in order to prevent any unrest.
Are ordinary people interested?
Most of the Nigerians I have met say they will indeed vote but they do not seem particularly enthusiastic.
One Lagos taxi driver told me that it was a waste of time voting because Mr Obasanjo was bound to win whoever people voted for.
There has been some progress under Mr Obasanjo but most Nigerians remain stuck in extreme poverty despite the vast oil wealth lying under the country's soil and off its coast.
How will the elections work?
Some 61 million people are registered. Six million names were declared to be fraudulent and struck off the voters' roll.
Very few have yet received their voters' cards - they are being told to get them as late as Saturday, before voting, in exchange for the paper slips they were given when they registered.
In order to win the presidential poll, a candidate must gain the most votes nationwide, as well as at least 25% of the vote in two-thirds of the 774 local government areas.
This is to ensure that a president has some support across the country and does not just represent one region or ethnic group.
If no candidate achieves that, there will be a run-off on 26 April.
Voting begins at 0800 local time (0700 GMT) and ends at 1500 local time for the elections at some 120,000 polling stations around the country.
Will it be free and fair?
After the parliamentary polls, the opposition says it suspects that rigging will be widespread.
The Independent National Electoral Commission (Inec) does not give the impression of being particularly efficient, but it says it has ironed out problems encountered a week ago.
This does not reassure people that everything will be above board and the newspapers are full of politicians accusing their rivals of planning to rig the polls.
One Western observer told me: "In the West, we would expect the results to give a 100% accurate indication of the voting."
"Here, we hope the election will be better than the last one."
He declined to put even a rough figure on how accurate these elections might be.
When can we expect the results?
Nigeria is a huge country, with some very poor communications.
Even a week after the parliamentary polls, some results are not yet in.
For the presidential election the results may well be known within three days, especially if it proves to be an easy victory for Mr Obasanjo.