Leading up to a U.S. presidential election, each state (and territory) must vote to decide which candidates it wants to compete in that election—but how exactly that decision happens differs from state to state. Some have primaries, while others hold caucuses.

A primary is a relatively straightforward process that resembles any other election. Essentially, you go to your designated polling station, which could be anywhere from a school to a sports complex, and check your favorite candidate on a ballot. Generally, any candidate who receives at least 15 percent of the votes is eligible to earn delegates, the elected officials who vote to decide whom to choose as the party’s presidential nominee at the national convention. Those delegates are then divided among eligible candidates in proportion to how many votes they earned. Since primaries are short and simple, almost all states and territories use them to help choose presidential nominees these days.

However, there are several holdouts that still opt for caucuses, a more manual (and more complicated) voting process with roots in late 18th-century American elections. During a Democratic caucus, participants arrive at a local venue and split up into groups based on which candidate they’re supporting; there’s usually a group for undecided voters, too. Volunteers count how many people are in each group, and—similar to primaries—any candidate who has at least 15 percent of the supporters is deemed “viable,” or eligible to earn delegates. Unlike primaries, caucuses don’t end after that initial tally. Supporters of candidates who didn’t meet the 15-percent threshold can then join groups for viable candidates; volunteers do a recount, and delegates are apportioned based on those updated numbers. Republican caucuses are similar, only the voting happens on an informal private ballot.

If your state holds a primary, there’s a pretty good chance you can get in and out without talking to more than a person or two—and it could even come as a surprise if someone tries to persuade you to vote for a certain candidate. At Democratic caucuses, on the other hand, that’s an integral part of the process. Before the initial count, people try to convince undecided voters to join their group (or supporters of a candidate who looks like they might not reach the viability threshold), and after the initial count, another wave of campaigning happens in order to claim supporters of unviable candidates. This, in addition to all the manual counting and re-counting, means that caucus attendees can count on being there for hours longer than primary participants.

Caucuses are a great way to see how citizens really feel about presidential hopefuls on a deeper, more personal level than polls and stats are often able to tell us, but the overall hassle—not to mention the fear of inaccurate vote-counting—has caused more and more states to switch to primaries in recent years. As Business Insider reports, there are only eight places that are still holding caucuses in 2020: Iowa, Nevada, North Dakota, Wyoming, Kentucky (Republican only), American Samoa, the Virgin Islands, and Guam.

Because Iowa’s caucuses are always first on the schedule, they’re often considered a little more important than some others—find out why here.

[h/t Business Insider]