First lady Michelle Obama, daughters Sasha and Malia, and a few reporters witnessed the intimate swearing-in ceremony, which took place in the Blue Room. Supreme Court Chief Justice John Roberts administered the brief oath of office.
The Constitution requires presidents to automatically begin their new terms before noon on Jan. 20. Because that date fell this year on a Sunday, a day on which inauguration ceremonies historically are not held, a second, public swearing-in is scheduled for Monday, which is Martin Luther King Jr. Day.
A crowd of up to 800,000 people is expected to gather on the National Mall to witness that event, which will take place on the Capitol's red, white and blue bunting-draped west front. Justice Roberts will administer the oath at that time as well.
Vice President Joe Biden was sworn in earlier Sunday at the Naval Observatory, his official residence. Supreme Court Justice Sonia Sotomayor administered the oath of office.
Mr. Obama launched a weekend of inaugural activities Saturday by heading up a National Day of Service. Along with his family, the president helped hundreds of volunteers spruce up a Washington area elementary school. He even picked up a paint brush and helped paint a bookshelf.
Beyonce will be back again for Mr. Obama's inauguration. Kelly Clarkson, Katy Perry and James Taylor are also scheduled to perform.
Danielle Wakefield of Costa Mesa was one of many Southern Californians who made the trip to Washington D.C. over the weekend to attend the inauguration.
"This is a bucket list item for me," she said. "This is something that once I do it, I don't know if I ever need to do it again, but I will be happy to have done it."
Whittier resident Darline Robles was at Mr. Obama's first inauguration and arrived over the weekend to be there for the second.
"I feel the same excitement," she said. "The crowds aren't as large, but that's OK. The excitement is still here. Every place I've gone, people are proud to be here, ecstatic, excited."
Eyewitness News Anchor Marc Brown also recalls being at Mr. Obama's first inauguration. He was standing in the middle of the crowd of 1.8 million who attended. It was an enormous crowd filled with hope.
"It was the most positive thing I've ever witnessed," Brown said. "It was the fact that he was African America, it was the fact that he was young and charismatic, it was the fact that he had an agenda that the majority of the country believed in."
Sen. Charles Schumer (D-New York), the chairman of the Inaugural Committee, said this inauguration is a new beginning for the country, Congress and the president.
"Four years ago was total excitement because it was a new president, first African-American president. Now, it's 'Let's get some things done.' And I am very hopeful that we can come together," Schumer said.
The 44th chief executive is only the 17th to win re-election, and his second-term goals are ambitious for a country where sharp political differences have produced gridlocked government in recent years.
Restoration of the economy to full strength and pressing the worldwide campaign against terrorists sit atop the agenda. He also wants to reduce federal deficits and win immigration and gun control legislation from Congress, where Republicans control the House.
"What we see in the second term is the real person who's in there," said Dr. Patrick James, international relations expert at the University of Southern California. "Because President Obama will not run for reelection, he's a lot more free to act as he wishes and without worrying, for instance, whether he's making some marginal members of his own caucus unhappy."
A fitting coincidence is that Monday is Martin Luther King Jr. Day. A black president is fulfilling an important part of King's dream.
"There's a certain symbolism there with President Obama, although interestingly enough, there's not been a lot of mention about either that fact or about his race," said Dr. Frank Gilliam, dean of the UCLA School of Public Affairs. "That stuff seems to have faded to the background a bit and what's come forward, of course is, the great issues that face his next term."
Security will be tighter than ever before, with 13,000 law enforcement officials working to keep the president and the crowd safe. More than 2,000 police officers from around the country were sworn in Sunday as deputy U.S. marshals.
Stay with ABC7 for special coverage of the inauguration. Eyewitness news anchor David Ono is in Washington. Look for his reports on Eyewitness News or get the latest by following him on Twitter and Facebook.