
Since 1972, the Iowa caucuses have been the first major electoral event of the nominating process for President. Although this will only result in the selection of about 1% of the nation's delegates, the Iowa caucuses have served as an early barometer of which candidates for president have political momentum.
Rather than going to polls and casting ballots, people gather at a set location in each of Iowa's precincts, often meetings in schools, churches, public libraries and sometimes even individuals' houses. In addition to the voting, caucus-goers also begin the formation of their parties’ platforms by passing policy resolutions. Republicans and Democrats each hold their own set of caucuses. Participants in each party's caucuses must be registered with that party. Persons 17 years of age or older can participate, as long as they will be 18 years old by the date of the general election. Observers are allowed to attend, but can not vote or participate in debates. Members of the media and campaign staff and volunteers attend many of the precinct caucuses. Youth who will not be eligible to vote by the date of the general election may also attend as observers.
Previously, Republicans conducted what was called the Iowa Straw Poll in August of the preceding year. This was generally a meaningless contest and the winner of the Straw Poll often failed to win the Iowa caucuses. In June 2015 the party announced that the Straw Poll would no longer take place. Recent changes to the Republican Party of Iowa's bylaws now make the caucus results binding on Iowa's delegates to the national convention. Starting in 2016, the caucus site voting, previously a non-binding poll, is now the binding method of selecting delegates, who in turn are bound to vote for candidates in proportion to the votes cast for each candidate at the caucus sites.

The process used by the Democrats is more complex than that of the Republicans. Each precinct divides its delegate seats among the candidates in proportion to caucus goers' votes. Then, for roughly 30 minutes, participants try to convince their neighbors to support their candidates. After 30 minutes, the supporters for each candidate are counted. For a candidate to receive any delegates from a particular precinct, he or she must have the support of at least 15% of participants. Once viability is determined, participants have roughly another 30 minutes to realign. Supporters of npn-viable candidates may find a viable candidate to support or choose to abstain. When the voting is closed, a final head count is conducted, and each precinct apportions delegates to the county convention. These numbers are reported to the state party, which counts the total number of delegates for each candidate and reports the results to the media. The delegates chosen by the precinct then go to a later caucus, the county convention, to choose delegates to the district convention and state convention. Most of the delegates to the Democratic National Convention are selected at the district convention, with the remaining ones selected at the state convention. The media declares the candidate with the most delegates on the precinct caucus night the winner, and little attention is paid to the later caucuses.
Current poll numbers (taken from the website www.realclearpolitics.com) show the following levels of support for the respective candidates:
Republican
Donald Trump: 32.7%
Ted Cruz: 26.9%
Marco Rubio: 12.6%
Ben Carson: 7.6%
Jeb Bush: 3.7%
Rand Paul: 3.7%
Chris Christie: 2.9%
Mike Huckabee: 2.3%
John Kasich: 2.0%
Carly Fiorina: 1.4%
Rick Santorum: 1.0%
Democratic
Bernie Sanders:46%
Hillary Clinton: 45.8%
Martin O'Malley: 4.3%

According to Politico, a small percentage of Iowans actually attend these caucuses. In 2012, for example, the turnout rate in the Republican caucus was 19.76 percent, meaning that 4 out of 5 people in Iowa who were eligible to vote in the caucuses didn’t bother to. In the 2012 Democratic caucuses just 4 percent of Iowa’s eligible voters gave their support to President Obama, while Mike Huckabee, the Republican winner, attracted the support of a mere 2 percent of Iowa adults.
Nonetheless, on Monday night these caucus results will attract a lot of media attention and in some cases they will make, or more likely break someone's campaign. Typically somebody drops out of the race based on a poor showing in Iowa. But it's the start of a process that will determine the major parties' nominees by this coming summer. Prepare to witness history.