JOE BIDEN
Who is he? Longtime senator from the small northeastern state of Delaware, and one of the Senate's leading foreign-policy heavyweights.
Joe Biden: Senate heavyweight
Why take him seriously? Top pollster Frank Luntz says Joe Biden's "poised and practiced oratory will keep him one of the front-runners and his definite stage presence will keep the public's attention". He also won praise from focus groups for his direct admission that he had been wrong to vote to give the president authority to go to war with Iraq.
What's going to stand in his way? Sen Biden is a famously rambling speaker who can sound like a professor lecturing students. And he dropped out of an earlier race for the White House when he admitted he had lifted lines from Neil Kinnock without crediting the British Labor leader.
Did you know? Joe Biden was elected to the Senate at the age of 29 - before he was even eligible to be a senator. He turned 30, thus meeting the age requirement, before he took his seat.
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HILLARY CLINTON
Who is she? Former First Lady now serving as senator from New York - the first former first lady to go on to hold elected office.
Hillary Clinton: Leader of the pack
Why take her seriously? Unbeatable name recognition and unmatched fundraising ability make Hillary - no surname necessary - the clear front-runner for the Democrats. She has tried to stake out a position as a centrist in her six years in the Senate - and has raised an estimated $40m for her Senate reelection campaign.
What's going to stand in her way? If Bill Clinton remains a divisive figure in American politics, that goes at least double for Hillary - some estimates say one in three Americans would never vote for her. And the US has never yet elected a woman president.
Did you know? Is there anything we don't already know about Hillary Clinton?
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JOHN EDWARDS
Who is he? Former lawyer and one-term North Carolina senator who ran for vice-president with John Kerry in 2004. He now runs an anti-poverty centre.
John Edwards: Southern charmer
Why take him seriously? Supporters and detractors alike agree that Mr Edwards is an excellent speaker, a man the Washington Post's politics blogger Chris Cillizza dubbed "the most naturally talented politician in the field". The Des Moines Register newspaper found in June 2006 that he led the field of likely Democratic contenders - ahead of Hillary Clinton - in Iowa, a critical state Mr Edwards has visited at least 10 times since the 2004 election.
What's going to stand in his way? Audiences - even sympathetic ones - tend to find Mr Edwards too slick. His poor-boy-made-good routine can also come across as patronizing.
Did you know? Mr Edwards helped to depose key witnesses during the Senate's impeachment trial of Bill Clinton in 1999.
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BARACK OBAMA
Who is he? Mixed-race junior senator from Illinois who shot to prominence at the 2004 Democratic National Convention.
Barack Obama: "Rock-star" reception
Why take him seriously? Time magazine dubbed Sen Obama "America's hottest political phenomenon", while television's own phenomenon, Oprah Winfrey, urged him to announce his candidacy on her show. A book tour just a month before the 2006 mid-term elections saw him greeted like a rock star - as did a trip to the critical state of Iowa to campaign for fellow Democrats.
What's going to stand in his way? Barack Obama will have served only four years in the Senate when the 2008 election rolls around - even less than John F Kennedy did before he was elected in 1960. And while his supporters praise him as thoughtful, deliberative and liberal, some experts doubt those are the characteristics that get a politician to the White House.
Did you know? Barack Obama's mother was from Kansas and his father was from Kenya - leading observers to suggest he is an African and an American, but not an African-American.
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BILL RICHARDSON
Who is he? Governor of the south-western state of New Mexico who was US ambassador to the United Nations under Bill Clinton before becoming his secretary of energy.
Bill Richardson: Relevant experience
Why take him seriously? Gov Richardson's resume may make him the ideal candidate in an age when voters are concerned about high gas prices and possible conflicts with Iran and North Korea. His Latino heritage may also win him votes with the country's largest minority population - one which both Republicans and Democrats need to compete for.
What's going to stand in his way? Gov Richardson is reportedly larger than life in small groups, easily able to connect with many different types of people - but in front of crowds he does not always demonstrate much charisma. And the small, out-of-the-way state of New Mexico is not a natural launching pad for a national campaign.
Did you know? Gov Richardson has been nominated for the Nobel Peace Prize four times.
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RUDOLPH GIULIANI
Who is he? Former mayor of New York City who shot to international prominence for his firm leadership on 11 September 2001.
Rudolph Giuliani: "America's mayor"
Why take him seriously? Mr Giuliani emerged as a hero of 9/11, prompting Time magazine to name him Man of the Year for 2001. Even before then, he was credited with bringing down New York's crime rate - and since leaving office he has been an active fundraiser and campaigner for other Republican candidates, keeping his stock high. He topped a June 2006 Gallup poll of likely Republican contenders, slightly ahead of John McCain.
What's going to stand in his way? "America's mayor" may be a law-and-order conservative, but his positions on gay rights, abortion and gun control are comparatively liberal, which does not endear him to the party's right wing. He has tried to make allies among the Christian right, but has not reversed his stance on the issues.
Did you know? Mr Giuliani was preparing to run against Hillary Clinton for a Senate seat in 2000 when he was diagnosed with prostate cancer, forcing him to quit the race.
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MIKE HUCKABEE
Who is he? Governor of Arkansas since 1996 best known nationally for his dramatic weight loss in response to a diagnosis of diabetes. Also named to Time magazine's list of the nation's best governors.
Mike Huckabee: Dramatic change
Why take him seriously? Gov Huckabee has carved out a place for himself as a health advocate following his own turnaround from fat to fit. As an ordained Baptist minister who says his faith is inseparable from his politics, he may be a magnet for conservative Christian votes - especially if competing against a social liberal such as Rudolph Giuliani.
What's going to stand in his way? His Evangelical faith has led him to take positions that do not appeal to all Republicans, such as an increase in the state's minimum wage - which drew fire from fiscal conservatives. It is also not clear that he can keep up with better-known names when it comes to fundraising.
Did you know? Gov Huckabee plays bass guitar in a band called Capitol Offense.
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JOHN McCAIN
Who is he? Maverick senator from Arizona who ran against George W Bush for the Republican nomination in 2000 and has had a complex relation with the president ever since.
John McCain: Straight talker
Why take him seriously? John McCain is one of the highest-profile figures in Washington, known for sponsoring key measures against torture and in favor of campaign finance reform.
He is known for his outspoken style - his 2000 campaign was dubbed the Straight Talk Express - which has not always won him friends in his own party. Although Sen McCain says unequivocally that he is a social conservative, his frequent skirmishes with the Bush administration have made him more popular with liberals than with conservatives.
Did you know? Shot down as a Navy pilot over Vietnam in 1967, Mr McCain refused to be released ahead of other prisoners of war - earning himself five years of captivity, two in solitary confinement.
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MITT ROMNEY
Who is he? Republican governor of Massachusetts who made headlines for the state's law making health insurance mandatory.
Mitt Romney: Olympics saviour
Why take him seriously? Gov Romney may have cracked one of the most intractable issues facing America - the millions of people with no health insurance in a country that does not have a national health system. He won acclaim for taking over the organization of the 2002 Salt Lake City Winter Olympics when planning looked on the verge of collapse, delivering a successful and profitable event. Washington insiders list him among the leading 2008 contenders in terms of money and organization.
What's going to stand in his way? It is not clear that Gov Romney's health-insurance model can be applied nationally, as Massachusetts is a small and wealthy state. Some voters may be put off by the fact that Gov Romney is a Mormon - a religion that some consider outside the mainstream. A Los Angeles Times/Bloomberg poll in July 2006 found that just over one in three Americans say they would not vote for a Mormon for president.
Did you know? Gov Romney's father, former Michigan Governor George Romney, ran for president in 1968, but failed to secure his party's nomination.
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SAM BROWNBACK
Sam Brownback, born September 12, 1956, in Kansas, senior Senator from that state. In April 2005, the Associated Press reported that Brownback, who is little known outside his home state, "is using a network of social conservatives and Christian activists to raise his profile" in such battleground states as Iowa and New Hampshire. He is well known for his social and fiscal conservative record, such as opposing abortion and instituting a flat tax alternative to the current IRS Code. He was also instrumental in Congress' bestowing the Congressional Medal upon Mother Teresa. In his own words, "The core of my being is to rebuild the family and renew the culture." On December 4, 2006, Brownback announced that he would form an exploratory committee.
On January 20, 2007 Brownback officially announced his candidacy. Of his campaign, Brownback has said, "I'm a son of a farmer from Kansas ... I still think anybody can be president. I don't think you have to show up with $100 million to do it. ... "I'm the tortoise in the race. And I don't like how the race starts; I like how it ends up."
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CHRISTOPHER DODD
Christopher Dodd, was born May 27, 1944, in Connecticut and is a five-term U.S. Senator from that state. Dodd was reported to be a likely contender for the Democratic Vice President slot on John Kerry's ticket in 2004. In May 2006, Dodd said he has "decided to do all the things that are necessary to prepare to seek the presidency in 2008", including hiring staff, raising money and traveling around the country in the next few months to enlist support.
On Jan. 11, 2007, Dodd announced his Presidential candidacy on the "Imus in the Morning" radio show with Don Imus
U.S. Senator from Connecticut: 1981–Present
U.S. Representative from the Connecticut's 2nd congressional district: 1975–1981
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FRED THOMPSON
Fred Dalton Thompson, born August 19, 1942, former Senator from Tennessee and actor, best known for playing D.A. Arthur Branch on Law & Order. There was speculation that Thompson would run for Governor of Tennessee in 2006, but he declined to run against the popular Governor Phil Bredesen. There has recently been a movement to encourage Thompson to run for President in 2008. On March 11, 2007, Thompson said "I'm giving some thought to it. Going to leave the door open. A lot of people think it's late already. I don't really think it is, although the rules of the game have changed somewhat. ... I think people are somewhat disillusioned. I think a lot of people are cynical out there. I think they're looking for something different."
On June 1, 2007, Thompson announced he had established a preliminary campaign committee, thus taking his first formal step toward an official presidential bid.
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REPUBLICANS
Sam Brownback
Rudy Giuliani
Mike Huckabee
John McCain
Mitt Romney
Fred Thompson
DEMOCRATS
Joe Biden
Hillary Clinton
John Edwards
Barack Obama
Bill Richardson
Christopher Dodd
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2008: The race begins
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