Most of the time, Iowa is a relatively low key state. Sure, it might occasionally pick up national attention when the state makes waves in the sports world with an undefeated college football team or when it became the third to legalize gay marriage back in 2009. But for the most part, Iowa keeps a low profile. Unless, of course, it’s a caucus year.

After months of hype, the Iowa Caucus is finally here. Tonight, registered Democrats and Republicans will gather at designated caucus locations to cast a hypothetical vote for their preferred candidates. But what are the rules of the Iowa Caucus and why exactly do we place so much importance on the opinions of a state with a relatively small population? Here’s what you need to know before you tune in for unrelenting caucus coverage tonight.

1. While Iowa residents have been caucusing since the 1840s, the state has only been “First in the Nation” since 1972. So what changed to make the Hawkeye State such a kingmaker?

According to Slate, Iowa switched their caucus from spring to January in the late 1960s to allow enough time between the caucus and the district convention (30 days) as well as between the district convention and the state convention (another 30 days). Much to New Hampshire’s chagrin, this calendar change meant that Iowa had trumped them as first to take a crack at picking November's presidential candidates. Democratic candidate George McGovern hit Iowa hard during the 1972 caucus and ended up showing surprisingly well. (He got second.) After he went on to take the party’s nomination, candidates started taking Iowa seriously—but New Hampshire still didn't. In 1988, Governor John Sununu angered a lot of Iowans when he said, “The people of Iowa pick corn, the people of New Hampshire pick presidents."

2. Iowa ranks 30th in terms of state population, and most of the time, only 20 percent of registered voters show up to caucus. An exception to that rule was the 2008 caucus, when the close Clinton vs. Obama race resulted in 239,872 Democratic caucus participants—about 40 percent of registered Democrats in the state.

3. Iowa is a “closed primary” state, which means participants have to be registered as Democrat or Republican in order to caucus. However, voters can register on the night of the caucus at their designated location.

4. Almost 1700 caucuses will be voting in Iowa, but multiple caucuses usually share the same location. The Democratic Party has about 1100 locations while the Republican Party has nearly 700. They can take place almost anywhere: churches, schools, fire stations, restaurants, even private residences. Where Iowans go to caucus depends on where they live, much like voting—but in many cases, the caucus location is not the same place as the voting location.

5. One major difference in the Republican and Democrat caucuses? The way they vote. Republicans cast secret ballots, sometimes using paper ballots, and sometimes just by scribbling their favored candidate's name on a scrap of paper. Democrats publicly declare their support and assemble themselves in groups according to the candidates they back. Undecided voters are usually then asked to take a side, with decided people making impassioned pleas for their candidates.

6. Another difference: Republicans can throw their support to whichever candidate they prefer, even the most unpopular ones. But Democratic candidates must receive a minimum of 15 percent of the votes in the room in order to remain viable. If a candidate doesn’t receive 15 percent, his or her supporters are asked to choose someone else. The process is dynamic, with friends and neighbors trying to convince those supporting an invalid candidate to come to their side.

7. Unlike primary voting, there is no mail-in absentee option. Only people who are physically present for the caucus may participate—with one exception, new just this year. For the first time ever, the Democratic Party is allowing Iowans living abroad and military members stationed outside of the state to telecaucus, while the Republicans have announced their own system. 

8. The Iowa caucus isn’t a surefire indicator of which candidate will go on to win the party nomination, but for Democrats, it’s a good predictor. Democratic winners since 1972 who went on to get the party nomination include Jimmy Carter, Walter Mondale, Bill Clinton (second term), Al Gore, John Kerry, and Barack Obama (both terms). That means Iowa only got it wrong when they picked Edmund Muskie, Dick Gephardt and Tom Harkin (a representative from Iowa).

9. When it comes to predicting the Republican nominee, however, Iowa’s accuracy rate plummets. Republican winners who got the party nomination include Gerald Ford, Ronald Reagan (second term), George H.W. Bush (second run), Bob Dole, and both of George W. Bush’s terms. They got it wrong when they picked George H.W. Bush against Ronald Reagan in 1980, Bob Dole in 1988, Mike Huckabee in 2008, and Rick Santorum in 2012.