US ELECTIONS: How does it all work?
You do not win the US Election by getting an overall majority.
Hillary Clinton won the popular vote by three million votes last time around but still lost overall.
That is because Americans vote for 538 members of the electoral college - delegates assigned to each state based on the number of Congressional and Senate seats they have.
These delegates then vote for the President
The candidate that gets the support of at least 270 electors wins.
Nearly 139 million people voted in the 2016 presidential election - a turnout of 55.5%.
At the same time as people are voting for a president, they will also be voting for some members of the House of Representativesi and Senators
Although voting is taking place today (Tuesday) because the US covers so many time zones, it is not until the following day that the last polls close.
Traditionally, the result is often known by the time polls close on the West Coast - about 11pm EST and 4am GMT.
It can be complicated trying to figure out when the winner has crossed the finish line because of the electoral college system, which allocates different numbers of votes depending on a state's share.
This year, though, concern has been raised about postal voting - which is expected to be considerably more important this time around because many people will prefer to mail in their ballot paper rather than visit a polling station in the middle of the ongoing pandemic.
Donald Trump has already said he has concerns that there could be voter fraud as a result.
If that were to happen, a legal challenge would be inevitable - with the conservative-leaning Supreme Court likely to make the ultimate call.
Whoever is victorious, assuming any challenge can be dealt with quickly, the winner would be expected to be approved by 6 January and inaugurated 14 days later.
If it is to be Joe Biden – then he would become, at the age 78, the oldest President to take office