But the election process can confuse many Americans, let alone foreigners used to parliamentary systems, absolute monarchies or dictatorships (you know who you are).
There are four different stages in the process that George Bush and his Democrat challenger John Kerry have to complete before either begins his term of office in 2005.
Aljazeera's electoral guide explains how you can become president of the world's only superpower.
Am I eligible?
You must be a citizen born within the US, Guam, Puerto Rico or the US Virgin Islands, or to American parents abroad. That rules out Arnold Schwarzenegger, the Austrian-born governor of California. You must also be a US resident for at least 14 years, and 35-years-old or above.
In practical terms, you should also have enormous sums of money. The Bush-Cheney ticket spent $186m campaigning in 2000, while the Gore-Lieberman duo spent $120m - and still lost.
You must be born American - and
raise a mountain of cash like Bush
This time round, Bush will have spent over $300 million and Kerry more than $270 million (including $75 million each of public funds) by the time November comes around.
What are primaries and caucuses?
This is the first stage of the election process. Each state holds primary or caucus elections between January and September where voters pick candidates of a particular party for the presidential poll in November 2004.
Reflecting the results, delegates will later go to their party's national convention with a pledge to vote for a particular candidate. So, in primary and caucus elections, voters are determining what percentage of a party's state delegates each candidate can rely on for support at the convention.
So what's the difference?
A primary is usually where voters registered with a particular party select a candidate from a list for that party. In such a "closed" primary election, for instance, only registered Democrats can vote in a Democrat primary.
But there are a few states that hold "open" primaries where a person can vote in any party's primary.
In contrast, caucuses are state conferences for party members. They gather, hear speeches and vote for delegates to represent candidates at the national convention. They are less common than primaries.
And national conventions?
This is where the Democrats and Republicans stress "party" in the term party politics. They are noisy, colourful, extravagant affairs, where delegates and candidates bash the opposition and sacrifice the opportunity to debate policies on the altar of public unity.
Kerry (L) and John Edwards rouse
Democrat delegates in Boston
Most delegates then vote for their pledged candidates. The exception is "unpledged" or "super" delegates, who make up 15% of the total. These include high-ranking party and elected officials such as governors and Congressional representatives, who can vote as they wish.
Because the results of each state's primary and caucus are already known, however, selecting a nominee at the national convention is often a formality.
In July, the Democrat convention in Boston endorsed runaway front-runner Kerry, who picked Senator John Edwards as his running mate.
With Bush practically unchallenged from within his party, the Republican national convention at the end of August will simply be a celebration of his presidency.
What happens next?
Many months, plane journeys and millions of dollars later, the candidates face voters in a nationwide poll on 2 November.
Al Gore spent $120m and won
most votes in 2000 - and still lost
Each state is treated as a constituency, so in practice presidential hopefuls need to win the election state by state.
As Al Gore found in the 2000 election, winning the popular vote across the country does not guarantee success.
After the votes have been counted, and states have been won by one candidate or the other, the matter falls into the hands of the electoral college.
The electoral college?
Each state appoints electors who gather to vote for a president and vice president in accordance with the wishes of their respective state's voters.
The number of electors each state sends matches the number of senators each has (always two) plus the number of House representatives. The District of Columbia is treated like a state and has three electors.
That adds up to 538 electoral college votes, so candidates must receive a majority of 270 electoral votes to become president and vice president.
In all states except Maine and Nebraska, the party that wins the most votes provides that state's electors, a winner-take-all scenario. Theoretically, an elector can vote for whomever he or she wants, but instances of "faithless" electors who ignore their state's wishes are rare.
Didn't 2000 have a fifth stage?
You're thinking of the US Supreme Court. Al Gore won most votes across the country, but he needed Florida's electors to have a majority in the electoral college.
A problem emerged in Florida because Bush's tiny lead among the state's voters seemed to result from some dubious ballot-counting practices and the fact that black voters who statistically would have voted for Gore had been disenfranchised.
Bush supporters hope for a less
controversial victory in 2004
Gore's supporters urged a recount amid accusations of vote-rigging, but then the Supreme Court – including judges appointed by Bush junior's father – stopped the recount and handed victory to his opponent. Florida's electors then cast all their votes for Bush.
Is that it?
There's just the swearing in ceremony left, which takes place on 20 January 2005.