These are Uganda's third general elections since the start of multi-party politics in 2005.
President Yoweri Museveni and his NRM party won landslide victories in the 2006 and 2011 polls. Observers said both polls were marred by irregularities and intimidation of opposition parties.
Museveni, 71, has been president since seizing power in a 1986 coup.
His main challengers in this year's vote, longtime opposition leader Kizza Besigye and former prime minister Amama Mbabazi, have seen election rallies broken up by police during the campaign.
Top issues this year include chronically high unemployment, corruption and Uganda's international role. At the final presidential debate, candidates discussed whether the country should continue sending troops to conflict areas like Somalia, and whether it should pull out of the International Criminal Court.
15 million Ugandans are registered to vote in the polls.