Voters will elect the President and Members to the House of Representatives and the Senate.
The elections were first scheduled to be held on February 14, 2015.
The Independent National Electoral Commission, INEC postponed it by six weeks to Saturday, March 28, 2015, citing security fears in the north-east region of the country, which the military says has largely been taken care of.
Article 134 Subsection 2 of the Nigerian Constitution stipulates that the a presidential candidate will be duly elected after attaining the highest number of votes cast, and has received at least a quarter of the votes at each of at least two-thirds of all the states and the Federal Capital Territory of Abuja.
If no candidate satisfies the requirement, a second election will be held between the two leading candidates within seven days from the pronouncement of the result.
Fourteen candidates will contest in the 2015 presidential election.
Nigerians will also today elect the candidates to occupy the 109 seats in the Senate.
The 36 states of the federation are each divided in three senatorial districts, each electing one senator, while the Federal Capital Territory elects only one senator.
950 senatorial candidates from the registered political parties will today, jostle to occupy the 109 seats in the Senate.
Elections to the lower House of Representatives representing the federal constituencies across the 36 states of Nigeria will also hold alongside the presidential and senatorial elections.
3,939 contestants across the 26 registered political parties will today jostle to occupy the 360 Federal Constituency seats at the polls.