The president says he will work in his second term to reduce the U.S. government's budget deficit, reform the tax code, reform the nation's immigration system and reduce America's dependence on foreign oil.
Obama congratulated his opponent on a hard-fought campaign and applauded Romney and his family for their tradition of public service. He says he will reach out to Republicans to seek solutions to the country's problems.
"In the weeks ahead I also look forward to sitting down with Governor Romney to talk about where we can work together to move this country forward," said Obama.
Former Massachusetts Governor Romney, speaking to supporters in Boston, conceded the election a short time earlier.
"I have just called President Obama to congratulate him on his victory. His supporters and his campaign also deserve congratulations," said Romney. "I wish all of them well, but particularly the president, the first lady and their daughters."
Romney says he and his running mate, Representative Paul Ryan, gave their all in the campaign and he thanked their supporters.
"I so wish that I had been able to fulfill your hopes to lead the country in a different direction. But the nation chose another leader and so Ann and I join with you to earnestly pray for him and for this great nation," Romney said. "Thank you and God bless America. You guys are the best. Thank you so much."
Obama won in the District of Columbia and 25 states, including the battleground states of Ohio, Virginia, Iowa, New Hampshire and Pennsylvania. Romney won in 24 states including North Carolina and Indiana, which both went for Obama last election.
Florida, another key battleground state, remains too close to call.
U.S. presidential elections are not decided by the popular vote, but by the Electoral College, in which each state's influence on the outcome approximates its population.
Both candidates made a final push for votes Tuesday, almost until the polls closed. .
Voters waited in long lines Tuesday at polling places. Some sporadic problems were reported, and both candidates dispatched lawyers to monitor the voting for irregularities.
The Justice Department had nearly 800 observers in 23 states to respond to any fraud allegations.
Meanwhile, Republicans retained control of the House of Representatives in Tuesday's voting, but Democrats blocked the Republicans' effort to take control of the Senate, where roughly one-third of the 100 seats were up for election.
Democrats will replace Republican senators in Massachusetts and Indiana, an independent will succeed a Republican in Maine, and in Connecticut, a Democrat will take the place of retiring independent Senator Joe Lieberman.
Japanese-born Democrat Mazie Hirono, who was elected in Hawaii, will be the first Buddhist U.S. Senator.
And, the Senate will have its first openly gay member, with the election of Democrat Tammy Baldwin in Wisconsin.