By Wesley Johnson, PA, in New York
The next president of the United States could be known in the early hours of November 5.
But the winner will not be officially elected until mid-December, and they will not take office until after an inauguration ceremony on January 20 next year.
The system used to elect the president stretches back to the very beginnings of the US, when the country won independence from Britain, but it has been widely criticised for enabling a candidate who loses the popular vote to win overall, as happened in 2000.
Under the electoral college system, each state has a number of votes which is linked to its number of members of Congress, and reflects its population.
The most populous state, California, has the most votes, 55, while other large states like New York and Florida have 31 and 27 respectively.
The least populated states, Montana, Vermont and Alaska, for example, have just three votes.
A presidential candidate needs 270 Electoral College votes - a majority of the 538 available - to win.
With two minor exceptions, all electoral votes are cast for the candidate that wins the state, no matter what the margin.
But the formal process does not take place on election day, November 4.
Instead, Americans cast their votes for their choice of president and vice president by voting for correspondingly-pledged electors, who then formally elect the president on December 15.
The two exceptions to this are Maine and Nebraska, which use a tiered system where a single elector is chosen within each Congressional district and two electors are chosen by state-wide popular vote.
The electoral college system was originally established to ensure individual states could maintain control over who was allowed to vote.
But it can distort the vote and has come in for criticism - in 2000, 1888 and 1876, the winning candidate failed to get the most votes in the nationwide popular vote but still won the presidency.
Nobel prize winner and former vice president Al Gore had 48.4% of the popular vote compared with George Bush's 47.9% but the Republican won more of the electoral college votes - 271 to 266 - and took the election.
The system is why certain so-called swing states are targeted more than others, especially in the final run-up to November 4.
But in the US a movement is under way to get rid of the electoral college and to award the presidency to the winner of the nationwide popular vote.
The National Popular Vote movement is aimed at preventing a repeat of 2000, and its supporters have asked states to change their laws to award their electoral votes to the candidate who wins the popular vote nationally.
John Koza, a Stanford University professor who is one of the idea's principal advocates, said the plan would help bring a national focus to presidential campaigns.
He said the current system encouraged parties to focus on a few contested "battleground" states, such as Ohio and Florida, and has exaggerated the significance of issues important to those states.
"Why is the rest of the country interested in Cuba? It's a couple of million people, we don't trade with them, and it's certainly been no military threat for 40 years," Mr Koza said.
The reason, he said, was that Florida, which has a large Cuban population, was a battleground state.
There have also been other attempts to change the electoral college system, but all of them foundered. They were aimed at amending the Constitution, an often drawn-out process that requires approval by Congress and ratification by at least 38 states, as opposed to introducing the bill state-by-state.
The proposal would also reduce the influence of small states and lead candidates to spend more time campaigning in voter-rich California, New York and Texas.
Once America has voted, the president-elect will prepare his administration and appoint officials as he gets ready to take control of the Oval Office after being sworn in, traditionally by the Chief Justice, at the inauguration ceremony on January 20.
His address that day is a key event in US politics, where the president sets out a vision and tone for the first four years of his administration.
Here is a list of the states and their electoral college votes:
:: Alabama 9 :: Alaska 3 :: Arizona 10 :: Arkansas 6 :: California 55 :: Colorado 9 :: Connecticut 7 :: Delaware 3 :: District of Columbia 3 :: Florida 27 :: Georgia 15 :: Hawaii 4 :: Idaho 4 :: Illinois 21 :: Indiana 11 :: Iowa 7 :: Kansas 6 :: Kentucky 8 :: Louisiana 9 :: Maine 4 :: Maryland 10 :: Massachusetts 12 :: Michigan 17 :: Minnesota 10 :: Mississippi 6 :: Missouri 11 :: Montana 3 :: Nebraska 5 :: Nevada 5 :: New Hampshire 4 :: New Jersey 15 :: New Mexico 5 :: New York 31 :: North Carolina 15 :: North Dakota 3 :: Ohio 20 :: Oklahoma 7 :: Oregon 7 :: Pennsylvania 21 :: Rhode Island 4 :: South Carolina 8 :: South Dakota 3 :: Tennessee 11 :: Texas 34 :: Utah 5 :: Vermont 3 :: Virginia 13 :: Washington 11 :: West Virginia 5 :: Wisconsin 10 :: Wyoming 3
