All you need to know on US mid-term election day, with news of key races, facts, quotes and pictures.
For the latest at-a-glance update each day, bookmark this page.
The introduction of new voting machines has caused problems for election workers and voters, with voting hours extended in some areas while others switched to using paper ballots.
Officials extended polling hours in Indiana, Pennsylvania, Georgia and South Carolina, after voting was held up by computer problems. Polling was also extended in parts of Illinois and North Carolina after voting stations opened late.
WHEN KEY POLLS CLOSE (GMT)
0000: Virginia and Indiana*
0100: Tennessee, Pennsylvania*, New Jersey, Missouri, Maryland, Illinois*, Florida, Connecticut
0200: Texas, South Dakota, Rhode Island, New York, Minnesota, Colorado
*Polling has been extended in some precincts
In Virginia, election officials contacted the FBI over complaints of voter intimidation by telephone.
Voters in East Coast states like New York and Connecticut were the first to cast their ballots when polls opened at 1100 GMT while people in Alaska will be the last to cast theirs, with polling stations in the far West due to stay open until 0600 GMT on Wednesday.
A national exit poll of 8,344 voters for the Associated Press suggests that about two-thirds of people said Iraq was a very important to deciding the way they voted.
Yet even more voters - about 80% - said the economy, government corruption and scandal were very important factors in their decisions.
Voting at his adoptive home in Crawford, Texas, President George W Bush appealed to all Americans "no matter what [their] party affiliation" to turn out for the election.
"Our government is only as good as the willingness of our people to participate in it," he said. He was
due back in Washington later to await the results.
The campaign - the most expensive for mid-term elections in US history - ended on Monday in a flurry of advertising in key battlegrounds, door-to-door canvassing thousands of phone calls to voters.
Some opinion polls suggested the Democrats' strong national lead over Mr Bush's Republicans had narrowed slightly, while others kept their lead in double figures.
The conversations you have today, the extra few minutes you take to bring someone who might not otherwise vote with you to the polls, the follow-up with your friends, family and neighbours to make sure they have voted - all of it will multiply the power of your single vote
Howard Dean, Democratic chairman, writing in an election day e-mail to party supporters
Laura and I urge you to vote Republican and to ask all your family and friends to go to the polls. The stakes are too high for you to stay at home
President George W Bush, writing in election day e-mail to Republican supporters
NUMBERS OF NOTE
Turnout may exceed previous mid-term elections, when it was about 40%, opinion polls suggest.
It may go above 42% though is unlikely to match the 1970 record of 47%, USA Today reports, quoting an American University estimate.
The National Association of Realtors (property sales agents) was the biggest donor in the race, according to the non-partisan Center for Responsive Politics, giving 53% of its $2,675,755 cash pot to the Republicans and the other 47% to the Democrats.
Other donors in the top five include the International Brotherhood of Electrical Workers ($2.18m) and
the National Beer Wholesalers Association ($2.16m).
The justice department has sent a record 850 poll-watchers to 69 cities and counties to safeguard against fraud, discrimination or system malfunctions in tight races.
Former Vice-President Al Gore was the last top Democrat to lend his campaigning weight to Ben Cardin, struggling to win a vital vacated Senate seat in Maryland against Republican challenger Michael Steele.
"They have brought in every heavy hitter they could think of... that says they know this seat is very much in play," said Steele spokesman Doug Heye after previous visits by Bill Clinton and Barack Obama.
Republican Senator George Allen was mobbed by reporters, supporters and protesters when he turned up at a subway station in Vienna, Virginia.
Democratic challenger Jim Webb rounded off his campaign with an appearance alongside Bill Clinton.
Mr Clinton also turned up in Rhode Island to endorse Democratic challenger Sheldon Whitehouse against Republican Senator Lincoln Chafee. Both candidates had spent the day canvassing in supermarkets and old people's homes.
New Jersey's Democratic Senator, Bob Menendez, said he scented victory as Republican challenger Tom Kean Jr continued to suggest he was corrupt.
"Too many people are giving up hope on the state of New Jersey," said Mr Kean. "That's not the New Jersey I grew up in."
In Montana, Republican Senator Conrad Burns predicted a "very close election" as opinion polls showed him with an even chance against Democratic rival Jon Tester.
For more, see our state-by-state map.
LA Times: Voters galvanized in a neck-and-neck nation
Wall Street Journal: Fund Raising Vies With Incumbency
Chicago Tribune: "It's in their hands"
For more commentary, see our mid-terms blog.
IMAGE OF THE DAY
Residents line up to vote outside a village hall in Hobart, Wisconsin