The 90-minute showdown in the US overnight was an attempt to persuade undecided voters to back them.
An estimated 100-million people tuned in last night possibly making it the most watched programme ever.
The debate focused on several key topics including race, foreign policy and crime.
Hillary Clinton also mentioned Donald Trump's tax returns – she suggested he might be deliberately keeping them secret.
Donald Trump used the debate to hit back at his Democratic rival.
He promised to make his finances public – but only if Mrs Clinton reveals e-mails she controversially sent from a personal account when she was Secretary of State.
Snap polls have declared Hillary Clinton the winner of the first presidential debate.
