The most-hyped presidential contest in the country also is among the most confusing.
The Iowa caucuses do not follow the conventional course of a traditional primary -- where, like in any standard election, residents walk into a polling site to cast their vote and walk out in a matter of minutes, crowd permitting.
By contrast, a caucus is a much more public and time-consuming affair.
Here's a guide to what Iowan caucus-goers will experience on Tuesday.
Where Are the Caucuses? All over the state. There are 1,774 precincts in Iowa, meaning 1,774 churches, libraries and other buildings where caucus-goers will converge Tuesday starting at 7 p.m. central time.
How Do the Caucuses Work? It's not just show up and vote. The caucuses are part poll, part GOP meeting. And unlike in a primary, supporters of particular candidates are allowed to campaign on site. In fact, it's part of the process. Before any votes are cast (and the term "vote" is used loosely here), supporters and surrogates of the various campaigns are permitted a few minutes to make the case for their candidate. This process means it's in every candidate's interest to have a speaker at all 1,774 caucus sites, as a way to sway uncommitted Iowans at the last minute.
After the speeches, those in attendance then write down their choice on a piece of paper. The results are counted, announced and fed to the media.
So Is That the End of Iowa's Electoral Duties? Nope. In fact, the caucuses on Tuesday don't even determine how many delegates each candidate receives at the national convention. That is a convoluted and multi-step process that only begins on Tuesday, which is more of a beauty contest, albeit a pivotal one.
Tuesday's caucuses will serve to elect delegates to the county conventions, where delegates will later be picked for district and state conventions, where delegates will finally be picked for the Republican National Convention. The caucuses are also used to pick local central committee members and discuss the party platform.
How Important Is This Iowa Contest, Anyway? Historically, Iowa does not have the best record of picking winners, at least on the Republican side. In the last five GOP primaries without an incumbent, the winner of the Iowa caucuses went on to win the nomination just two times - in 1996 and 2000.
However, political analysts generally agree that it's very important to place roughly in the top three in Iowa. The only GOP nominee since 1972 who did not finish in the top three in Iowa was John McCain in 2008.