David Jackson, USA TODAY
President Obama claimed victory early Wednesday morning by telling supporters "the task of our union moves forward," and its challenges will be met.
"We know in our hears that for the United States of America, the best is yet to come," Obama told backers in Chicago.
He later said: "Tonight, you voted for action --not politics as usual."
Obama thanked his family and friends, and also paid tribute to vanquished Republican opponent Mitt Romney.
Striking a bipartisan note, Obama said he is willing to sit down with Romney and talk about ways "to move this country forward."
At another point, Obama said, "despite our differences, most of us share the same hopes for our nation." He cited better education, new energy development, and reducing the federal debt.
The "best campaign team ever": and an army of volunteers who delivered turnout also came in for presidential praise.
1:35 a.m. -- President Obama and his family are on stage, as speakers play Stevie Wonder's Signed, Sealed, Delivered (I'm Yours).
12:56 a.m. -- Mitt Romney has conceded the presidential race to President Obama.
"I have just called President Obama to congratulate him on his victory,": Romney tells supporters in Boston.
Romney also thanks wife Ann, saying "she would have been a wonderful first lady."
Saying "I believe in America," Romney seeks a bipartisan tone. In congratulating Obama, Romney says he will "pray for him, and pray for this great nation."
11:25 a.m. -- It's official: Barack Obama has been re-elected as the 44th president of the United States
The president claimed victory over Mitt Romney after winning the pivotal state of Ohio, tweeting his supporters: "This happened because of you. Thank you. We're all in this together. That's how we campaigned, and that's who we are. Thank you. -bo"
A crowd at a Chicago convention center began cheering and dancing after the Ohio call, as The Supremes' You Can't Hurry Love over loudspeakers.
The Associated Press officially called the race at 11:39 p.m.
While Romney still held a lead in the popular vote, Obama is on the track to win as many as 300 electoral votes, and perhaps more; it takes 270 to win a presidential election.
Romney is expected to speak tonight at a convention center in Boston; Obama will follow him with remarks in Chicago.
11:19 p.m. -- President Obama wins Ohio, closes in on a second term.
Aides for Obama and Mitt Romney saw Ohio as the key to the election.
Some outlets have projected an election win for Obama; the crowd in Chicago is going crazy.
11:11 p.m. -- Two new Associated Press calls: President Obama wins New Mexico, Mitt Romney takes Missouri.
Obama now has 234 electoral voters -- closer to a clinching 270. Romney has 200.
11:07 p.m. -- President Obama is at the Fairmount Hotel in downtown Chicago, mingling with staff members; we're told they are upbeat and confident.
Obama leads Mitt Romney in electoral votes, 229 to 190.
With about half the vote counted, Romney leads in popular votes, 50%-48%.
11:00 p.m. -- The biggest state of all weighs in: California goes for President Obama; he now leads in electoral votes.
Obama now has 229 electoral votes, only 41 shy of the 270 needed to win; Mitt Romney is projected at 190 electoral votes
The Associated Press also awards Obama his home state of Hawaii and Washington state; Mitt Romney takes Idaho.
The AP also says Obama will win Minnesota, another state where Romney had hoped to pull an upset.
10:55 p.m. -- Mitt Romney gets a once-swing state: North Carolina, the state where President Obama held his re-nominating convention.
Four years ago, Obama became the first Democrat since Jimmy Carter in 1976 to win North Carolina in a presidential state. now the Tar Heel State has flipped back to the Republicans.
10:50 p.m. -- Mitt Romney wins Arizona, the home of 2008 GOP nominee John McCain. He also wins Nebraska, which normally goes Republican.
The challenger still leads President Obama in both popular and electoral votes, narrowly.
10:43 p.m. -- Exit polls illustrate one of the biggest issues working against Mitt Romney: George W. Bush.
About half the voters still blame President Obama's Republican predecessor for the nation's economic troubles; Romney, of course, sought to blame Obama.
Another stat: Voters are divided on the direction of the country; 46% say it's headed in the right direction, while 52% believe it is still headed in the wrong direction.
10:20 p.m. -- For you social media mavens, it's now official -- This election is the most tweeted event in history; more than 20 million Twitter messages.
10:04 p.m. -- The first swing state falls: New Hampshire goes for Obama.
It's a small state to be sure -- only 4 electoral votes -- but the Granite State was one of the nine or so battleground states that both sides fought for; Romney has a home there.
Romney still leads the electoral vote, 159-147; New Hampshire is a good sign for Obama, as the two candidates battle for states like Ohio and Virginia.
The challenger also leads the popular vote with 25.2 million votes, or 50 percent; Obama had 24.2 million, or 48 percent, with 32 percent of precincts in.
10:02 p.m. -- Mitt Romney wins Utah, another red state.
9:53 p.m. -- Big state for President Obama: Pennsylvania goes for him, projects the Associated Press.
Mitt Romney had hoped for an upset in the Keystone State -- he even campaigned there on Tuesday -- but it went Democratic for the sixth straight election. Pennsylvania has 20 electoral votes.
George H.W. Bush, in 1988, was the last Republican to carry Pennsylvania.
No swing states have been called -- but that could change soon.
9:30 p.m. -- More factoids from exit polls:
President Obama is winning the empathy race: 53% of voters said Obama is more in touch with people like them, compared to 42% for Romney.
There also appears to be a generation gap: A majority of those under 45 years old backed by Obama, especially voters under 30; people 45 years and older are going for Romney.
9:22 p.m. -- The red and blue states continue to fall in line -- New Jersey (whacked last week by Hurricane Sandy) goes for President Obama.
Arkansas, now more Republican in the post-Bill Clinton era, goes for Mitt Romney. So does Mississippi, one of the nation's most conservative states.
Romney leads the Electoral College 158-104, but each candidate has only won states they were expected to -- no swing states have been called yet.
9:15 p.m. -- Some exit poll numbers are rolling, and, not surprisingly, the economy is rated the top issue.
Nearly 6 in 10 voters (59%) listed the economy as their top issue, ahead of health care (18%), federal debt (15%), or foreign policy (5%)..
About 4 in 10 blamed President Obama for economy, and almost all of them voted for Mitt Romney. But the other half of the respondents blamed former President George W. Bush for the economy, and Obama racked up among those voters.
9:05 p.m. -- More poll closings and more state projections -- none a surprise.
President Obama takes the blue state of New York as well as the more purplish Michigan -- the state where Mitt Romney was born.
Mitt Romney carries the more conservative states of Nebraska, Wyoming, Kansas, Louisiana, South Dakota, Texas, and North Dakota.
Other states have been added to the too-close-to-call list, including Colorado and Wisconsin. They join Ohio, Virginia, and Florida on the list of key battlegrounds that will decide this race later tonight.
8:54 p.m. -- An update on the race from our friends at the Associated Press:
Mitt Romney led in the popular vote, gaining 8.2 million votes, or 52 percent, to 7.5 million or 47 percent for President Obama, with 5 percent of the precincts tallied.
Romney also held an early electoral vote advantage, 76-64, with 270 needed for victory.
Obama carried Connecticut, Rhode Island, Vermont, Maine and Romney's home state of Massachusetts. Also, as expected, he won Delaware and Maryland as well as the District of Columbia and Illinois.
Romney had Alabama, Georgia, Tennessee, South Carolina, Oklahoma, Kentucky and West Virginia in his column. He also won Indiana, a state Obama carried in 2008 but did not contest this year.
8:38 p.m. -- Tennessee goes for Mitt Romney, the Associated Press reports -- and re-takes the Electoral College lead over President Obama, 67-64.
Also note: Romney lost his home state of Massachusetts -- unusual for a presidential nominee, but not surprising this year given the Democratic proclivities of Massachusetts.
Close states still out though: Florida, Ohio, and Virginia. Once one of those is decided we'll have a better handle on the race.
8:32 p.m. - All eyes are on Ohio, where President Obama has a taken pretty big lead, but it's still too early to project.
It's hard to see how Mitt Romney wins without Ohio.
Virginia and Florida also remain too close to call -- Romney probably has to win both of those as well.
8:16 p.m. -- It's absurdly early, but: Republican Mitt Romney leads the popular vote by 52%47%, though only 5% of the vote is in.
President Obama, meanwhile, has grabbed an electoral vote lead of 64-40 -- though no state is a surprise, and the two are locked in close battles in Ohio, Florida, and Virginia.
Many analysts wondered if he would have another 2000 situation, when one candidate won the popular vote and another won the electoral vote. It's early, but still ...
8:10 p.m. -- A slew of blue states are called for President Obama: His home state of Illinois, Connecticut, Delaware (Joe Biden's home), Maine, and the District of Colombia.
Mitt Romney, meanwhile, takes the red state of Oklahoma
8:00 p.m. -- There are a raft of final poll closings -- including Florida, where President Obama and Mitt Romney are locked in a close contest, just as they are in Virginia.
Polls are also now closed in Pennsylvania -- a state where Obama is favored, but where Romney made a late pitch.
Also note another state that may take a while to call: North Carolina. Romney's people had been very confident about the Tar Heel State, Obama's not-so-confident. As of now, however, they're in a dead heat.
7:56 p.m.-- The Associated Press calls the very Republican states of Indiana and South Carolina for Romney; with 11 and 8 electoral votes.
Romney leads in electoral votes 32-3, but none of the called states are a surprise.
7:50 p.m. -- The polls are closed in what may be the key state of the election: Ohio. And, as in Florida and Virginia, the race between President Obama and Mitt Romney is much too close to call.
Settle in -- this could be a long night.
7:35 p.m. -- Another no surprises: The Associated Press calls West Virginia and its 5 electoral votes for Romney.
So far, Romney leads in electoral votes by 13-3 -- but it's very early.
7:20 p.m. -- Some of the votes are starting to trickle in from Florida, and -- doesn't this sound familiar? -- Obama and Romney are virtually tied at 50%. This looks like a long night, just like the one George W. Bush and Al Gore had in 2000 -- largely because of Florida.
Remember, some of Florida is the central time zone -- the state's final poll closing isn't until 8 p.m.
7:00 p.m. -- The polls close in Virginia, and, as expected, it is way too close to call -- and will probably stay that way for a while. Big state in the Obama-Romney race.
Meanwhile, the Associated Press calls Vermont for President Obama -- 3 electoral votes.
Kentucky and its 8 electoral votes go to Romney.
No surprises there.
6:45 p.m. -- We're waiting for the first wave of final state poll closings at 7 p.m., and one of them is pivotal: Virginia. The winner of the closely contested Old Dominion will have a huge leg up in the presidential race, and we'd be surprised if a call is made right away.
Four years ago, Obama became the first Democratic presidential candidate since Lyndon Johnson in 1964 to take Virginia.
Other 7 p.m. poll closings are more predictable. Georgia, Indiana, Kentucky and South Carolina are seen to be leaning in Romney's direction; Obama is the favorite in Vermont.
6:30 p.m. -- Romney -- who campaigned today in Ohio and Pennsylvania -- will be watching the returns with his family in Boston.
The Republican presidential candidate told reporters he has written a 1,118-word victory speech (no one talks about writing concession speeches).
Romney also said he has no regrets: "I feel like we put it all on the field. We left nothing in the locker room. We fought to the very end, and I think that's why we'll be successful."
6:15 p.m. -- The Obama campaign has sent us some info on the president's evening here in Chicago:
"This afternoon, the girls flew into Chicago after school along with their grandmother, Marian Robinson. Tonight, the First Family will have dinner together along with Mrs. Robinson. This evening, the First Lady's brother, Craig and his family will join the Obamas and the President's sister, Maya and her husband to watch the Election night returns."
Sounds like a good time, though there may be a little anxiety.
Obama, by the way, spent the day in his home city of Chicago, where he did television interviews and played basketball with friends.
6 p.m. -- For campaigns, this is the longest day.
While waiting for actual votes to be tabulated, the candidates and their aides have to listen to tales of turnout, long lines of voters, malfunctioning machines, and exit polls.
But it will be over soon -- unless the election is too close to call, in which case things might last well into Wednesday, or even beyond.