Monday’s debate will be the first showdown between Republican presidential nominee Donald Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE and Democratic nominee Hillary Clinton Hillary Diane Rodham ClintonJoe Biden looks to expand election battleground into Trump country Biden leads Trump by 12 points among Catholic voters: poll The Hill's Campaign Report: Biden goes on offense MORE as polls tighten with fewer than 50 days until the election.

It's expected to be one of the most-watched debates in history, so here's everything you need to know about the highly anticipated match-up.

What time does it start?

The debate begins at 9 p.m. and is scheduled to last for 90 minutes, with no breaks.

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The debate will be held at Hofstra University in Hempstead, N.Y. The university has previously hosted presidential debates in 2008 and 2012.

Who is moderating?

NBC’s Lester Holt will be the moderator. This will be the "Nightly News" host's first time moderating a presidential debate.

Holt faces pressure as the first moderator of the general election cycle and the challenge of wading through a likely unpredictable debate. His colleague, Matt Lauer, got ripped by fellow media members and both campaigns when he hosted a recent presidential forum.

Trump has also been vocal about Holt’s upcoming performance. The GOP nominee said he respects Holt but falsely accused him of being a registered Democrat and warned of unfair debates. Trump also advised Holt not to fact-check.

What topics will they cover?

The three topics announced are “Securing America,” “America’s Direction” and “Achieving Prosperity," which signal the debate will largely hinge on questions surrounding national security and the economy.

At least 30 minutes of the debate will be focused on national security. The debate comes in the wake of two bombings in New York and New Jersey as well as a stabbing in Minnesota.

What are the rules?

The debate will have six 15-minute segments, with two segments focusing on each of the three topics. Trump and Clinton will each have two minutes to respond to questions posed by Holt.

Who is carrying it?

The debate will air on all of the broadcast and cable news networks as well as C-SPAN, Univision and PBS.

It will also be streamed online, and Hofstra University has provided a list of outlets that will likely stream it.

What's the size of the debate audience?

The debate will be held in the David S. Mack Sports and Exhibition Complex, which is a 5,023-seat arena on the university’s campus.

The debate commission won’t know the size of the audience until Monday, after the set is complete and the fire marshal signs off. A Hofstra spokeswoman estimated there will be about 1,000 people in attendance. Hofstra University students can receive tickets through a lottery system, and the parties and campaigns also get a number of tickets they can divvy out.

For those who can’t attend, some experts predict that more than 100 million people could be watching, the largest audience in presidential debate history.

What does the debate mean for Clinton and Trump?

Clinton goes into Monday with a narrow polling advantage, but the race has tightened since both parties held their conventions.

Debating is Clinton’s strong suit, but she faces the difficulty of going toe-to-toe with Trump, who was known for personal attacks and veering away from policy during primary debates. The former secretary of State has prepared for different versions of Trump’s personality.

Trump also has a lot to prove during Monday’s debate as he tries to showcase a more presidential and professional side. He’ll have to show he can keep up with Clinton’s knowledge and flex his foreign policy muscle especially with the first debate’s heavy emphasis on national security issues.