Former Speaker of the House of Representatives
This thrice-married 68-year-old started the impeachment drive against President Bill Clinton over his affair with Monica Lewinsky. The author of two dozen books, Gingrich is known as a policy innovator who constantly attacks the Democrats in films, on TV and with his speeches
Currently Texas Congressman
It is the third time that this anti-war 76-year-old is making a bid for the White House. A libertarian-minded Republican who believes in small government, he has criticised interventionist foreign policies and monetary policies pursued by the US Federal Reserve.
Former Governor of Massachusetts
Consulting and venture capitalism
The current frontrunner but not ahead by a clear margin, the 64-year-old father of five only won the Iowa caucuses by 8 votes. He failed to win the Republican nomination in 2008 and is criticised for his liberal track record in Massachusetts but claims he can win over Democratic and independent voters.
Former Republican Senator for Pennsylvania
The 53-year-old father of seven represents the socially conservative wing of the Republican party. He is strongly anti-abortion, against gay rights and gay people serving in the military. He was only nine votes short of winning the Iowa caucuses and is endorsed by media magnate Rupert Murdoch.