President Barack Obama has defeated his Republican challenger Mitt Romney to win a second and final term in office.
Romney conceded the long, hard fought 2012 campaign in a speech before a crowd of disappointed supporters in Boston, Massachusetts, the state he once governed. Standing alone on the podium, he congratulated Obama on his election victory, saying "this is a time a great challenge for our nation, and I pray the president will be successful in guiding our nation."
Romney also praised his vice presidential running mate, Congressman Paul Ryan, calling him "the best choice I've ever made" next to marrying his wife Ann.
Supporters at the president's campaign headquarters in Chicago waved flags and cheered at the news late Tuesday, which came after Obama won enough states to reach the 270 electoral votes needed to clinch the election.
Obama's campaign staff Tweeted "Four more years," and included a picture of the president hugging his wife, Michelle Obama. The Empire State Building in New York lit its light atop the iconic building blue, the color of the Democratic Party.
The latest projected results have Obama, a Democrat, winning 303 electoral votes and Romney with 203 Electoral College votes.
The projections say 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 23 states including North Carolina and Indiana, which both went for Obama last election. Another key battleground state, Florida, remains too close to call.
The candidates made a final push for support Tuesday as voters waited in long lines at polling places. Some sporadic problems were reported, and both candidates dispatched lawyers to monitor the voting for any irregularities.
The Justice Department had nearly 800 observers in 23 states to respond to any allegations of fraud.
After a year-and-a-half of campaigning, three debates and thousands of televised campaign ads, nationwide pre-election surveys had the two candidates in a virtual deadlock.
U.S. presidential elections are not decided by the national popular vote, but rather by the Electoral College system, developed more than 200 years ago, in which each of the 50 states' influence on the outcome is roughly equivalent to its population.
Voters were also electing all 435 members of the House of Representatives, and 33 of the 100 members of the Senate.
Projections Tuesday show Republicans will hold onto control of the House of Representatives while Democrats will stay in charge of the Senate.
Millions of Americans cast ballots in early voting in the last month. Obama voted several days ago in his home city of Chicago, and spent Tuesday there. He conducted interviews for broadcast in key states and played basketball with friends, one of his Election Day traditions. He also called voters from a campaign office.
Romney, a one-time venture capitalist, voted Tuesday morning in Massachusetts, the northeastern state he once governed but where Obama won. He also made a final push for votes in the key states of Ohio and Pennsylvania.