After the longest, most expensive election campaign in US history, voters are about to elect the 44th president.
Republican John McCain and Democrat Barack Obama have returned to their home states of Arizona and Illinois to vote and hold final rallies.
Mr Obama is holding a steady lead in final opinion polls and record numbers of voters are expected to turn out.
In the first voting of the day, Mr Obama defeated his rival by 15 votes to six in Dixville Notch, New Hampshire.
The town, which has a 60-year tradition of being first in the nation to vote, opened its polls at midnight, with turnout of 100%.
George W Bush won there in 2004 on his way to re-election. It was the first time the town had voted Democrat since 1968.