UPDATE: 10:50 p.m. EDT -- The debate ended with moderator Lester Holt probing Donald Trump on his remarks that Hillary Clinton, the first female major party nominee for president, "doesn't have a presidential look." Trump denied he had ever said that, but Clinton wasn't about to let him off the hook.
"He tried to switch from 'look' to 'stamina.' But this is a man who has called women pigs, slobs and dogs. And someone who has said pregnancy is an inconvenience to employers," Clinton said. "Who has said women don't deserve equal pay unless they do as good of a job as men. And one of the worst things he said was about a woman in a beauty contest—he loves beauty contests—supporting them and hanging around them. And he called this woman Miss Piggy. Then he called her Miss Housekeeping because she was Latina. Donald she has a name. Her name --"
Trump jumped in: "Where did you find this? Where did you find this? Where did you find this?"
Clinton went on: "...is Alicia Machado. And she has become a U.S. Citizen... And you can bet she's going to vote this November."
Trump had a long reply. "Hillary is hitting me with tremendous commercials. Some of it is entertainment, some of it—somebody who has been very vicious to me, Rosie O'Donnell. I said very tough things to her and I think everybody would agree that she deserves it and nobody feels sorry for her. But you want to know the truth. I was going to say something extremely rough to Hillary and to her family and I said to myself, I can't do it. I just can't do it. It's inappropriate. It's not nice. But she's spent hundreds of millions of dollars on negative ads on me, many of which are absolutely untrue. They're untrue and they're misrepresentations and I will tell you this, Lester, it's not nice and I don't deserve that," he said.
UPDATE: 10:33 p.m. EDT -- The U.S. needs a leader who will stand up to bullies, Hillary Clinton said during the presidential debate.
"Words matter. Words matter when you run for president - and they really matter when you are president," she said.
Donald Trump said Clinton was to blame for the Islamic State group for not stopping them before they declared a caliphate in Syria and Iraq.
UPDATE: 10:24 p.m. EDT -- Donald Trump denied that he supported the Iraq war before he made Hillary Clinton's support for the war an attack line during the 2016 White House race.
"The best person in her campaign is mainstream media," Trump said.
Trump said he has "a winning temperament" and Clinton does not.
"I have a much better temperament than she does," Trump said.
UPDATE: 10:18 p.m. EDT -- Hillary Clinton said the biggest challenges facing the next president are cybersecurity and cyber warfare, and called out Donald Trump for supporting the Iraqi war before denouncing it.
UPDATE: 10:06 p.m. EDT -- Hillary Clinton called Donald Trump's years-long battle to paint President Barack Obama as a non-citizen, "a racist birther lie."
"He has a long record of engaging in racist behavior and the birther lie was very hurtful. Barack Obama is a man of great dignity and I can tell how much it bothered him and annoyed him that this was being touted and used against him," Clinton said.
Trump said Clinton treated Obama poorly during the 2008 Democratic primary. "When you try to act holier than thou, it really doesn't work," Trump said.
UPDATE: 9:59 p.m. EDT -- Hillary Clinton and Donald Trump both received about 18 minutes of speaking time during the first half of the debate, CNN reported. At one point, Trump made a joke about Clinton staying home in recent days. She said she had stayed off the campaign trail to prepare for the debate.
"You know what else I prepared for? I prepared to be president and I think that's a good thing," Clinton said.
UPDATE: 9:50 p.m. EDT -- Donald Trump said minorities need stop and frisk public safety programs and better community relations with police departments to stop violence in cities.
"We need law and order," he said. "African Americans and Hispanics are living in hell."
Hillary Clinton said Trump needs to stop portraying black communities in such a negeative light, prompting him to sigh in disagreement.
"Stop and frisk was found to be unconstituitional in part because it was ineffective," she said.
UPDATE: 9:42 p.m. EDT -- Donald Trump said he would release his tax returns when Hillary Clinton released her missing emails from her stint as secretary of state in the Obama administration.
Clinton said if Trump was going to point to his business as his claim to the White House, the nation should discuss his debt and bankruptcies.
"It's all words," Trump said of Clinton's claims. He said the government doesn't know how to buy or spend.
International Business Times explained Trump's bankruptcies here.
UPDATE: 9:29 p.m. EDT -- Well, that quickly got nasty. Hillary Clinton and Donald Trump yelled over each other for a few minutes during the debate as they discussed free trade, terrorism and climate change.
Asked about manufacturing jobs from overseas, Trump said: "The first thing you do is don’t let them leave."
But Clinton wanted more specific policy plans. "At least I've got a plan to fight ISIS," Clinton told Trump.
"You've been doing this for 30 years, why are you just starting to think of solutions now?" Trump said. "No wonder you’ve been fighting ISIS your entire adult life."
Clinton responded by telling fact-checkers to get to work. "Join the debate by saying more crazy things," Clinton said after noting that Trump was going to blame her "for everything." He shot back, "why not?"
UPDATE: 9:13 p.m. EDT -- The first topic of the debate is jobs. Donald Trump said foreign nations are stealing the U.S.' jobs and companies. Hillary Clinton said it was her granddaughter's birthday and she wanted to create a future with a strong economy that also balances gender equity and paid family leave.
Clinton sought to contrast her blue-collar upbringing against Trump's wealthy roots.
"Donald was very fortunate in life. He really believes the more you help wealthy people, the better it will be. I don't buy that," she said.
"My father gave me a very small loan," Trump countered of the $1 million loan his father gave him to start his business empire.
Later he asked Clinton if he could call her "Secretary Clinton." "I want you to be very happy," he said.
UPDATE: 9:06 p.m. EDT -- It's finally happening! Hillary Clinton and Donald Trump walked on stage and greeted each other Monday night before the debate. "How are you doing, Donald," Clinton said. She wore a red pantsuit. He wore a blue tie.
UPDATE: 9:03 p.m. EDT -- Moderator Lester Holt opened the debate Monday night by acknowledging the potential audience of 100 million viewers. "That thud you heard backstage was the sounds of my knees buckling," he joked.
Meanwhile, former House Speaker Newt Gingrich set the bar high when he tweeted that Donald "will pass the test of being adequately competent & will get a big boost in acceptability."
Melania Trump, wearing a formfitting black dress, shook hands with Bill Clinton before the debate kicked off.
UPDATE: 8:54 p.m. EDT -- Hillary Clinton could be the first woman president, but what about Bill Clinton? He was poised to become Monday the first former president to watch his spouse in a presidential debate. He tweeted: "Looking forward to tonight's debate knowing that millions of Americans will see the @HillaryClinton I've known for over 40 years."
UPDATE: 8:48 p.m. EDT -- Hillary Clinton is the first woman to become a major political party's presidential candidate, which mean this is the first time a woman has represented a major political party during a presidential debate.
UPDATE: 8:40 p.m. EDT -- This is the third time Hofstra University in New York has hosted a presidential debate. The school saw applications for admission climb by 6.3 percent after it hosted the 2012 debate.
UPDATE: 8:22 p.m. EDT -- More Americans believe Hillary Clinton will trounce Donald Trump in Monday night's debate rather than vice a versa, according to a recent CNN/ORC poll. Promoter Don King, a Trump supporter, told reporters backstage that the debate was "the biggest fight I've ever promoted. This is a fight for liberty."
UPDATE: 8:10 p.m. EDT -- There will be no commercials during the presidential debate Monday night, but that doesn't mean advertisers aren't trying to make some money off the hype. German luxury car maker Audi and other brands paid high prices for commercials airing during the pre- and post-debate coverage, the Wall Street Journal reported.
UPDATE: 7:50 p.m. EDT -- Donald Trump and Hillary Clinton have two more debates to go before the Nov. 8 election. The next presidential debate will be moderated by ABC's Martha Raddatz and CNN's Anderson Cooper on Oct. 9 in St. Louis and the final debate on Oct. 19 will be held in Las Vegas. The vice president candidates will debate once on Oct. 4.
UPDATE: 7:32 p.m. EDT -- Libertarian presidential candidate Gary Johnson and his running mate, Bill Weld, will be live tweeting the debate between Hillary Clinton and Donald Trump live from Twitter's headquarters in New York City, according to their campaign website.
The duo "will be making themselves available to the media, watching the debate with great interest, and will be anxious to point out how a third voice, representing millions of independent voters disenfranchised by the Republican and Democrat parties, would better serve the American people," spokesman Joe Hunter told ABC News.
Johnson was excluded from the debate at Hofstra University in Hempstead, New York, because his poll numbers were too low. Read more about Johnson's debate night here.
UPDATE: 7:22 p.m. EDT -- Bernie Sanders said the media should stop talking about a candidate's debate style. He said reporters often declared Hillary Clinton the winner during the Democratic debates, when online viewers would instead name him their favorite. Sanders said during an interview with CNN Monday that he hoped the debate between Clinton and Republican Donald Trump will focus on real issues.
"She doesn't need my advice," Sanders said.
UPDATE: 6:48 p.m. EDT -- The latest polls show Hillary Clinton and Donald Trump locked in a tight race for the White House. Quinnipiac University called the race "too close to call" Monday, with Clinton leading Trump by a margin of 47 percent to 46 percent. A Monmouth University poll found Clinton with 46 percent support.
Donald Trump's showbiz performances during the 11 GOP primary debates helped him outlast popular Republican figures such as Florida Sen. Marco Rubio, former Florida Gov. Jeb Bush and Ohio Gov. John Kasich. He did it with cheap insults, semi-witty catchphrases and vague policy statements. Oh, and who can forget that one time he boasted about his penis size?
But will his reality TV persona work against Hillary Clinton Monday night during the first presidential debate?
"The big question tonight is whether these tactics, which elevated him from a field of 16 candidates, will work as well against just one. Trump is an expert at standing out from a crowd, not taking on a sole opponent," Libby Nelson of Vox wrote Monday.
For her part, Clinton, who ran for the Democratic presidential nomination in 2008 against President Barack Obama, is also a debate champion. Or at least that's what GOP leaders are telling the media to help set expectations low for Trump.
"The expectations on Hillary are very, very high," Republican National Committee Chairman Reince Preibus told Fox News. "She’s been doing this for 30 years. I think people expect her to know every little detail."
International Business Times has you covered on all things debate and election related. Before the debate starts at 9 p.m., catch up on the campaign trail with some of our recent guides on the 2016 race to the White House: