The pair clashed bitterly on the campaign trail, which included three presidential debates.
Mr Trump called his opponent a liar and a "nasty woman" and repeatedly said she can't be trusted.
Mrs Clinton attacked him over his ability to do the job and the allegations of groping, which he denies.
"Donald thinks belittling women makes him bigger," she said.
Hillary Clinton has spent a fair bit of time in the White House before.
She served as US secretary of state under Barack Obama and she is a former first lady.
She is 69.
Donald Trump is better known as a businessman and TV star.
During his career, Trump has built office towers, hotels, casinos and golf courses.
He is 70.
And he wants to build a wall between the US and Mexico
Hillary Clinton's use of private email caused a huge row
When Mrs Clinton started working as secretary of state seven years ago, she sent both work and personal emails from the address firstname.lastname@example.org.
Using her own server meant she had total control over her messages.
As such, she could decide what information should or shouldn't be passed on to government.
Meanwhile, Donald Trump was accused of sexual assault by a number of women
During the second presidential debate, Mr Trump was asked if he had ever grabbed anyone's genitals or kissed them without consent.
He replied: "Women have respect for me. And I will tell you: No, I have not."
These voters in San Antonio have been chatting to Radio 1 Newsbeat about who they will be voting for and why.
And we spoke to people in the UK about they would vote... if they could
Current polling puts Trump and Clinton neck and neck.
Most states nearly always vote the same way, leaving a handful of battleground states where the election will be won and lost.
Play the game to find out more about these key states and see who you think will win the election.
Predict the president: Will Clinton or Trump win the US election? You decide
The US uses the electoral college system to elect its president, in which each state is given a number of votes based on its population.
A total of 538 are up for grabs.
The magic number is...
The result will be announced...
...by around 5am in the US.
This means America's next president should be named by 10am in the UK, so long as whoever loses concedes.