Here's what you need to know about the big night in US politics:
When and where
Wednesday. 6pm (Thursday 12pm AEDT), at the University of Nevada, Las Vegas.
Duration: 90 minutes
Format
The two candidates will each be standing at a lectern, as they were in the first debate.
There will be no commercial breaks in the broadcast.
Where to watch
Most major US networks will carry the debate on their channels and websites (main networks ABC, NBC, CBS, Fox and PBS; cable networks CNN, C-SPAN, Fox News, Telemundo; and websites such as Facebook, Hulu, Huffington Post, Politico, Twitter and Yahoo).
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Themes
The debate will be divided in 15-minute segments, dedicated to the following themes: debt and entitlements; immigration; economy; Supreme Court; foreign hot spots; and fitness to be president.
Moderator
Chris Wallace, a 69-year-old veteran political reporter for Fox News, the most watched news network in the United States. He's expected to be tough on both candidates.
Ratings to beat
First debate on September 26: a record 84 million television viewers, according to Nielsen.
Second debate on October 9: 66.5 million viewers
