President Mahamadou Issoufou is running for a second term in an election critics say has been marred by unfair practices. The poor but resource-rich former French colony faces a host of problems.
The 63-year-old Issoufou hopes to beat 14 challengers in the first round of voting on Sunday so as to avoid a second round runoff.
Opposition parties have agreed to back whoever gets the most support among them in the event of a runoff in a bid to kick Issoufou out of power.
Issoufou has campaigned on meeting pledges to increase growth and improve infrastructure.
Security is also a major issue. Niger is faced with Islamist militants in neighboring Libya and Mali, and Boko Haram terrorism stemming from Nigeria.
'Politically motivated charges'
A front-runner among the opposition is Hama Amadou, the head of the Nigerien Democratic Movement (NDM), who is in jail after being arrested upon his return from exile in France last November.
The former prime minister and speaker of parliament faces charges over his alleged involvement in a baby-trafficking ring - charges that opposition figures say are politically motivated.
Another top name is Seini Oumarou, a former prime minister to ex-President Mamadou Tandja, who was overthrown in a coup in 2010. Oumarou, who like Tandja, is from the National Movement for the Society of Development (NMSD), came in second place to Issoufou in the 2011 presidential election.
Also among the top contenders is the country's first democratically elected president, Mahamane Ousmane, who is running for the fourth time since his 1993 election.
In a controversial move, Niger's constitutional court on Saturday approved a government plan to allow voters without IDs to cast a ballot, as long as two other people vouched for their identity.
The opposition cried foul at the proposal, which could fuel tensions and allegations of voting irregularities following a presidential campaign already marred by claims of intimidation against the opposition.
The nation of 18 million is one of the poorest on the planet despite being rich in uranium, gold, iron and oil. Nearly two-thirds of the population live on less than two dollars a day and corruption is rife.
The landlocked Sahel country has been plagued by instability and coups - including an alleged failed coup attempt in December - since becoming a multiparty democracy in 1990.
Parliamentary elections are also being held.
The outcome of the vote will be announced within five daysof the polls closing on Sunday.
cw/tj (AFP, Reuters)