Welcome to BBC's live page of the first presidential debate between President Barack Obama and Republican challenger Mitt Romney. We'll bring you all the insights from our correspondents at the event in Denver, as well as a selection of your e-mails and tweets.
The head-to-head begins at 19:00 local time (02:00 BST) and runs uninterrupted for 90 minutes, focusing on domestic policy, including the economy and healthcare. It is the first of three presidential debates and a vice-presidential one before the election on 6 November.
And here's our candidates...
No, you haven't been transported to an alternate reality: two University of Denver students - Zach Gonzales (left) and Dia Mohamed - stood in earlier for the former Massachusetts governor and current US president during a rehearsal and camera test.
Recent polling suggests Obama has maintained a slight lead nationally as well as in several key election states (our poll tracker has the big picture). A crash-and-burn by either candidate tonight could really hurt his approval rating.
Pundits say Obama must ensure he doesn't damage his buoyant likeability ratings, while bringing the attack to Romney. The New York Times has reported that aides are encouraging Obama to use humour and his wide smile, and to avoid coming across as smug.
Romney has reportedly been equipped with an arsenal of "zingers" - the one-line put-downs that leave spin-doctors drooling and YouTube creaking.
1843 Adam Blenford, BBC News, Denver
With 15 minutes to go, the audience have taken their seats and are being given a stern warning about keeping their phones off and refraining from cheering and applause throughout the debate.