Democrats in the Midwest state of Iowa will get the chance to pick from candidates vying to unseat President Donald Trump in the first Democratic primary race on Monday.
There are currently 11 Democratic candidates. One of them - billionaire Michael Bloomberg - has decided to skip the early voting states, so is not competing in Iowa.
Among the Democrats polling at the top are senators Bernie Sanders and Elizabeth Warren, former vice president Joe Biden and Pete Buttigieg, a former mayor.
The Iowa caucus is important as it sets momentum for the races in more populous states.
The four early primary states in February are all building up to what is known as Super Tuesday, on March 3, when 14 states and other jurisdictions, including powerhouses California and New York, cast their votes.
Iowa, a relatively small state with a population of just 3 million, uses a caucus system unlike any other in the country to vote for its candidates.
Instead of casting private ballots, voters gather at school gymnasiums, libraries and other locations around the state and form groups that align with their preferred candidate.
If any group of voters is less than 15 per cent of the total, then that candidate is considered "unviable" and the group members will realign to other candidates or seek to join forces with another unviable candidate.
