Hillary Clinton and Donald Trump have been criss-crossing America in a final push for votes before election day.
Both have held rallies in the battleground states of North Carolina, Pennsylvania and Michigan.
Mrs Clinton urged voters to back a “hopeful, inclusive, big-hearted America” while Mr Trump told supporters they had a “magnificent chance to beat the corrupt system”.
Polls give Democrat Mrs Clinton a four-point lead over Republican Mr Trump.
A record number of Americans – more than 46 million – have voted early by post or at polling stations.
There are signs of a high turnout among Hispanic voters, which is believed to favour Mrs Clinton.
Due to the US having six different time zones, polling opens and closes across the country at different points.
It will generally start at 6am Eastern Time, which is 11am in the UK, and begin to close at 7pm – which is midnight here.
The last state, Alaska, won’t have closed its polls until after 4am our time, but there should be a good idea of who has won by this point.
The first votes will be declared just after midnight on the Tuesday, so actually six full hours before polls open.
Dixville Notch in New Hampshire races to be the first every year, with residents gathered in a ski resort ballroom ready to vote at midnight. There is tough competition from other small towns across New Hampshire to beat them, though.
Despite Dixville Notch’s speedy declaration, those wanting to see the results come in are in for a long night.
When will we find out who has won?
No one yet can know when the next President will be announced for certain, but the earliest the election will be called in favour of either candidate is 11pm ET time – so a bleary-eyed 4am in the UK.
A concessions speech by the losing party will follow after, when it is clear which side has won.
There is, however, the possibility of there being no outcome by the end of election day itself. The result could be too close to call, there could be legal debates that delay results or cause recounts, or there may even be a tie.
UK Times (including key states):
Midnight – Polls start to close, including Florida, Georgia and New Hampshire. Exit poll predictions will start being announced.
12:30am – Ohio and North Carolina close
1am – Pennsylvania and Michigan close
2am – Arizona and Wisconsin close
3am – Iowa and Nevada close
4am – All polls other than Alaska have closed
After 4am – It’ll start to become clear who has won. Last year, Obama was called for at 4:48am.
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