Date of caucus: 3 January Election polltracker Full state profile Q&A: US primary elections

Barack Obama and Mike Huckabee won the Iowa caucuses, giving them significant boosts to their nomination campaigns.

Republican Mr Huckabee defeated his nearest rival, Mitt Romney, while Democrat Barack Obama secured a clear victory over John Edwards, relegating Hillary Clinton into third place.

The victory for Mr Huckabee is seen as a blow for Mr Romney, who spent tens of millions of dollars more on his campaign.

The main Democratic contenders all spent large amounts of time and money in Iowa.

Despite her setback, Mrs Clinton vowed to continue to fight to secure the Democratic nomination, as did second placed John Edwards.

Republican frontrunner Rudy Giuliani decided to limit his Iowa expenditure and spend more in larger states like Florida.

Iowa is a largely agricultural state and candidates rarely voice opposition to farm subsidies.

Using opinion polls to predict the result of the caucus is notoriously difficult, because of the state's complex voting system and the likelihood of a low turnout.

But Iowans take very seriously their state's role as the first-in-the-nation test for presidential candidates, and voters take a great interest in every aspect of the candidates' platforms.