As the 2020 presidential nomination season kicks off in February, it won’t start with a primary — where voters go to their polling place and cast a secret ballot — but with caucuses. While the vast majority of states hold primary elections, a few use these more complicated events to show their preferences for candidates.

In recent years, some states have ditched caucuses for primaries, but Iowa, Nevada and Wyoming are holdouts. So why choose a caucus?

Party caucuses have been used in various forms in the United States since the 1800s to address a range of political topics. In Iowa’s case, caucuses not only allow activists and voters to make a case for their preferred candidate, but also to talk about issues that could be incorporated into the state party platform, said Dennis Goldford, a political science professor with Drake University in Iowa.

They also attract enthusiastic party members. Caucusing requires passion and a strong connection to a particular candidate, in contrast to the simple and private act of marking a ballot in a primary. “[The Iowa caucuses] make candidates and potential candidates talk to voters as real, live, individual human beings,” Goldford said. Candidates meet with voters in a more personal way, he added, rather than using them as “campaign props.” Especially in early caucus states, a relatively small group of people wields a lot of power to influence average voters around the country.

But the dedication and time needed to participate means that not everyone can. And the sometimes arcane rules about how caucuses operate and how delegates are awarded can result in confusion about an influential aspect of our democracy.

As Iowa prepares to hold its first-in-the-nation caucuses on Feb. 3, here’s what you need to know:

What is the difference between a primary and a caucus?

Primaries and caucuses differ primarily in how they are funded and operated. State governments typically run primaries, which allows the state to dictate the parameters, such as who can participate. For instance, some states have closed primary contests that only allow registered party members to vote; open primary elections allow unaffiliated voters to participate as well.

Caucuses are meetings between registered party members, run by the political parties themselves. Since 2016, at least 10 states have switched from caucuses to a primary system. In Kansas, for example, Democrats have opted for a “party-run primary,” which has elements of a secret ballot vote and a caucus.

What happens at a caucus?

In each caucus state, Republicans and Democrats set their own rules, which can vary greatly, and produce some drama over how the results are calculated. In 2016, confusion over the narrow results out of the Iowa caucuses between Sen. Bernie Sanders and Hillary Clinton upset some Sanders supporters.

Zeroing in on Iowa, registered Republicans will gather on a weeknight at more than 1,000 locations around the state. During the night, attendees will write down and submit their preferred candidate, as well as choose delegates to send to county conventions.

Iowa’s Democratic procedure is much more involved. Registered party members also convene at about the same number of precincts around the state, and attendees at each location are asked to split into groups based on their preferred candidates. Undecided members can also form a group. The individuals in each group are then counted, and typically candidates that receive at least 15 percent of the head count are considered “viable” or eligible to receive delegates.

Next, caucus-goers have the chance to “realign,” a 15-minute period during which members can try to convince others to join their group.

New Democratic rules for 2020 state that only members of nonviable groups can realign; they can either join an already viable group, or combine to help a nonviable candidate reach the 15 percent threshold. All the candidates who meet the 15 percent cutoff will be awarded delegates based on a formula put together by the Iowa Democratic Party.

These delegates go on to county conventions throughout the state. Later, at Iowa’s state-wide Democratic convention, delegates for the Democratic National Convention will be chosen. Delegates for the Republican National Convention are also picked at a state convention.

Both the Democrat and Republican Nevada caucuses operate in similar ways to Iowa, though the GOP canceled its 2020 caucuses as a show of support for President Donald Trump.

What do critics say about presidential caucuses?

Presidential caucuses are frequently criticized for their complex rules and time commitment, which narrows who can participate. In a primary, voters have a wider window of opportunity — let’s say between 7 a.m. and 8 p.m. — to choose when they go to their polling place. Caucusing can be an hours-long process that takes place at one designated time on a weeknight. These restrictions can limit participation from shift workers, caregivers, parents and others.

This year, Democrats have proposed new options to give more voters an opportunity to support their chosen candidate. Both the Iowa and Nevada Democratic Parties proposed holding “virtual caucuses,” using a phone system in addition to the regular events. That measure was blocked by the national party, citing security concerns. Instead, Nevada Democrats will offer an in-person, early voting period, in addition to the main caucuses. And Iowa will have “satellite caucuses,” which would operate like the others, but take place at 99 locations that seek to better accommodate people like students, seniors and foreign-language speakers.

Iowa’s prominence as the first nominating contest has been criticized for not being racially and culturally reflective of the entire country, yet still playing a big role in determining who gets nominated. (Iowa’s population is about 85 percent white, while the national average is about 60 percent — excluding those who identify as Hispanic in the Census.) To address this, the Nevada caucuses were moved up earlier. The Western state — with a population that is about 48 percent non-Hispanic white — now has the third presidential nominating event.

Early caucuses in Iowa and Nevada, particularly the more procedurally complicated ones hosted by Democrats, have also faced accusations of flawed organization and poor management.

2020 may further test the process, as Democrats brace for anticipated higher voter turnout, a large field of candidates and adjusted rules on reporting results. In Iowa, rather than reporting only the state delegate equivalent numbers, as is customary, Democratic precincts will also report two raw counts — one for the statewide headcount total for each candidate after the first alignment , and one for the final alignment. This could result in public pushback over the winners.

Former 2020 Democratic presidential candidate Julián Castro has been an outspoken critic of the Iowa caucuses, expressing concerns over diversity and the procedural restrictions. He has also suggested reordering the Democratic primaries and caucuses with more diverse states earlier in the schedule.

“People would think that Republicans designed the Iowa caucus,” Castro told MSNBC this month. “I don’t believe that we should have these caucuses.”

Over the years, caucuses have strayed from the initial model of promoting debate and persuasion among voters, says David Fott, a political science professor at the University of Nevada, Las Vegas.

“People tend to come in with their minds made up and then leave with their minds made up,” Fott said. “There’s no real attempt to win over other people. … You might as well have a primary. It’s quicker. I don’t get the sense that there’s a benefit from making people stay longer to cast their preferences.”

Why do the caucuses in Iowa and Nevada get so much attention?

Simply put, early states receive more attention because they are the first indications of where real voters stand on the candidates outside of public polling. While New Hampshire and South Carolina provide the first real elections, caucuses also offer insight from more knowledgeable, politically active members of the party.

These early results receive national news coverage and analysis. Candidates who do well receive more positive attention, boosting voter and donor confidence in their electability.

The true competition, however, is between the candidates and public expectation, Goldford said. Someone finishing in first place as expected isn’t as much of a draw as an underdog story, he added. “You could finish second or even third, but if you had been nowhere, that’s a major ‘man bites dog’ story,” Goldford said. For example, if Sen. Amy Klobuchar, D-Minn., “were to come in that top three, that would be a major story,” he said.

A candidate who exceeds expectations in Iowa has sometimes won it all. An unexpected victory by Jimmy Carter at the 1976 Iowa caucuses changed their significance in the nomination process. The surprising outcome propelled Carter from a little-known Georgia governor to the White House. A more modern example is Barack Obama, who faced off against Hillary Clinton’s name recognition and political experience and won Iowa in 2008. He did not win the New Hampshire primary, but still secured the Democratic nomination and later the presidency.

Since Carter’s victory, Iowa has fiercely protected its vaunted position as the first state; even presidential candidates have defended its status.

In 1996, Louisiana Republicans leapfrogged ahead in the calendar, holding caucuses in a small town called, fittingly, Iowa. But the leading GOP candidates boycotted the caucuses in Iowa, Louisiana, to avoid angering voters in the state of Iowa.

Despite other proposals to switch up the order, Iowa’s prominent place is unlikely to change anytime soon.