London - Factbox explaining how the voting system will work at the FIFA presidential elections in Zurich on May 29.
Who can stand?
According to FIFA guidelines, a candidate has to have played an active role in association football for two of the five years preceding his proposed candidature.
The candidate has to present declarations of support from at least five of FIFA's member associations, although these associations do not have to vote for the candidate they backed.
The deadline for candidates to register was Jan. 29. The candidates were all subject to "integrity checks" by FIFA's ethics committee.
The 209 member associations of FIFA each hold one vote. This means tiny associations such as Brunei, Sao Tome and Principe and Andorra hold the same voting rights as the likes of Germany, Italy and Brazil.
FIFA has set up an independent committee, officially known as the "Ad Hoc Electoral Committee" to supervise the process.
The ballot is held in secret, even if there is only one candidate. This differs from soccer's European governing body UEFA, for example, where Michel Platini, the only candidate for re-election in March, was voted in "by acclamation".
Before the ballot, each candidate can address the Congress for 15 minutes.
To be elected in the first round, a candidate must obtain two-thirds of the votes cast.
If this does not happen, a second round is held round is held. This time, a simple majority (ie more than 50 percent of the votes) is sufficient for a candidate to be elected.
If no candidate gets a majority, the candidate with the least votes is eliminated and a new round is held. This continues until one candidates obtains a majority.
If there is only one candidate, the a simple majority is sufficient in the first ballot.