Presidential elections are decided by the Electoral College, not by popular vote. Barack Obama earned the necessary amount of Electoral College votes for reelection shortly before midnight.
Many are still curious how the popular vote ends up. Obama seems poised to win that too in 2012, though it may take some time before that's official.
As of this writing, Obama had a 58,720,700 (50.1%) to 56,145,950 (48.4%) lead on Mitt Romney for the popular vote.
(UPDATE: As of 2:30 p.m. ET on Wednesday, Obama has widened his popular vote lead. He now leads 60,193,076 or 50.4% to 57,468,587 or 48.1% with nearly all precincts reporting. Still no official word yet, however.)
(UPDATE (2): As of Noon on Friday, with nearly all votes in, Obama assuredly will win the popular vote, leading Romney by a count of 61,173,739 or 50.5% to 58,167,260 or 48.0%. At this point, a few final votes are being counted and then all that's left is for the results to be officially certified.)
Romney led the popular vote for most of the night, but that was before the western United States had their polls closed and ballots counted. Population centers in California and other western states are boosting Obama's numbers significantly.
Nate Silver posted to the New York Times at 2:31 a.m. Wednesday morning that Obama is "likely" to win the popular vote, "perhaps by two to three percentage points, once votes from California, Oregon and Washington are fully counted."
How has the popular vote finished in other recent presidential elections? In 2008, Obama/Biden topped McCain/Palin in the popular vote 69 million to 59 million. In 2004, Bush/Cheney defeated Kerry/Edwards in the popular vote 62 million to 59 million. In 2000, Gore/Lieberman won the popular vote over Bush/Cheney 50.9 million to 50.4 million, yet lost the election due to the Electoral College.
You can find the latest popular vote count on our Election Results page.