The US president has a huge influence on people’s lives both at home and abroad, so when the next election is held on 3 November, the outcome will matter to everyone.
The US political system is dominated by just two parties, so the president always belongs to one of them.
The Republicans are the conservative political party in the US and their candidate in this year’s election is President Donald Trump, who is hoping to secure another four years in power.
The Democrats are the liberal political party in the US and their candidate is Joe Biden, an experienced politician best-known for serving as Barack Obama’s vice president for eight years.
Both men are in their 70s – Mr Trump would be 74 years old at the start of his second term, while at 78, Mr Biden would be the oldest first-term president in history.
How is the winner decided?
Both candidates compete to win electoral college votes.
Each state gets a certain number of electoral college votes partly based on its population and there are a total of 538 up for grabs, so the winner is the candidate that wins 270 or more.
This means voters decide state-level contests rather than the national one, which is why it’s possible for a candidate to win the most votes nationally – like Hillary Clinton did in 2016 – but still be defeated by the electoral college.
All but two states have a winner-takes-all rule, so whichever candidate wins the highest number of votes is awarded all of the state’s electoral college votes.
Most states lean heavily towards one party or the other, so the focus is usually on a dozen or so states where either of them could win. These are known as the battleground states.
Who can vote and how do they do it?
If you’re a US citizen and you’re 18 or over, you should be eligible to vote in the presidential election, which takes place every four years.
However, lots of states have passed laws requiring voters to show identification documents to prove who they are before they can vote.
These laws are often put into place by Republicans who say they’re needed to guard against voter fraud. But Democrats accuse them of using this as a form of voter suppression as it is often poorer, minority voters who are unable to provide ID like a driving licence.
How people vote is a contentious issue this year because of the coronavirus pandemic. Some politicians are calling for wider use of postal ballots, but President Trump has said – with very little evidence – that this could result in more voter fraud.
Is the election just about who is president?
No. All of the attention will be on Trump v Biden, but voters will also be choosing new members of Congress when they fill in their ballots.
Democrats already have control of the House so they will be looking to keep hold of that while also gaining control of the Senate.
If they had a majority in both chambers they would be able to block or delay President Trump’s plans if he were to be re-elected.
All 435 seats in the House are up for election this year, while 33 Senate seats are also up for grabs.
When will we find out the result?
It can take several days for every vote to be counted, but it’s usually pretty clear who the winner is by the early hours of the following morning.
In 2016, Donald Trump took to the stage in New York at about 3am to give his victory speech in front of a crowd of jubilant supporters.
But don’t set your alarm clocks just yet. Officials are already warning that we may have to wait longer – possibly days, even weeks – for the result this year because of the expected surge in postal ballots.
The last time the result wasn’t clear within a few hours was in 2000, when the winner wasn’t confirmed until a Supreme Court ruling was made a month later.
When does the winner take office?
If Joe Biden wins the election, he wouldn’t immediately replace President Trump as there is a set transition period to give the new leader time to appoint cabinet ministers and make plans.
The new president is officially sworn into office on 20 January in a ceremony known as the inauguration, which is held on the steps of the Capitol building in Washington DC.
After the ceremony, the new president makes their way to the White House to begin their four-year term in office.