How the 2024 Republican and Democratic presidential primaries and caucuses work

The race for the White House is on, as the 2024 presidential primaries and caucuses began earlier this month.

Here's how the 2024 Republican and Democratic presidential nominating contests work.

Who is running in the presidential primaries and caucuses?

Former President Donald Trump and former U.N. Ambassador Nikki Haley are the remaining major Republican candidates seeking their party's presidential nomination through the primaries and caucuses that each state holds. (Past candidates include Florida Gov. Ron DeSantis, South Carolina Sen. Tim Scott, former Vice President Mike Pence and others.)

Meanwhile, Minnesota Rep. Dean Phillips and author Marianne Willamson are mounting long-shot campaigns to challenge incumbent President Joe Biden for the Democratic nomination as he seeks a second term.

Robert F. Kennedy Jr. initially launched a campaign as a Democrat, too, but then switched to being an independent.

What is a presidential primary and when did the primaries start?

The goal for both Democratic and Republican candidates is to win their respective presidential nominations, which will put their names on the ballot for November's general election.

Third parties, like the Libertarian Party, hold their own nominating contests; independent candidates must instead go state-by-state to fulfill the requirements of getting on the ballot in November.

Party nominations are won via state-level primaries or caucuses, which are similar -- but notably different -- contests.

First, primaries:

A presidential primary is an election held every four years in the months before a party's presidential convention.

The rules for each primary can vary somewhat state by state. But broadly speaking, during a primary, voters choose who they would prefer to become a party's nominee for the general election -- casting ballots in a state's Republican primary, for example, or the Democratic one or the Libertarian one, but not all of them.

Some states require voters to be registered with a given party to participate in that nominating contest; some states don't require this.

Based on the results of a primary, candidates receive a certain amount of delegates, who are people who pledged to support that candidate at the party's national convention where the nomination is awarded.

Technically speaking, that means candidates are competing for delegates rather than just the most votes.

But since the advent of the modern nominating system, in the '70s, delegates have become more closely tied to whomever wins the most votes.

For Republicans, how many delegates a candidate earns depends on the state. In some, the winning candidate in the primary takes all of the delegates, while in others the delegates are awarded proportionally to how much of the vote the candidate received.

For Democrats, in all of the primaries, the delegates are awarded proportionally based on how much of the vote the candidate received, although candidates must earn at least 15% of the vote in that state to be able to earn any delegates.

Presidential nominations did not always work this way. Before the 1970s, primaries and caucuses were not held as often or in a systematic fashion and would often award candidates far fewer delegates.

While they let candidates prove to undecided party officials that they could be viable in general elections, party leaders and insiders ultimately held much more sway over who got on the ballot rather than the average voter.

But in 1968, Vice President Hubert Humphrey won the Democratic presidential nomination without having entered a single primary. The chaotic convention and politics that resulted helped spark the reforms by both major parties that led to the current nominating process.

The calendar of U.S. presidential primaries and caucuses began this year with the Iowa caucuses on Jan. 15 and with the New Hampshire primaries on Jan. 23.

What is the definition of a caucus, and how is a presidential primary different from a caucus?

In some states, the state Republican or Democratic Party is holding caucuses instead of a primary to determine who voters there would prefer as the party's nominee. The most high-profile caucuses were in Iowa earlier this month.

While both primaries and caucuses award delegates to candidates, the caucuses work differently than primaries.

Caucuses, like primaries, can have rules that vary by state and party. Unlike primaries, caucuses are run by political parties and not in conjunction with state election officials.

Broadly speaking, at a caucus, like the many held across Iowa, voters gather at a public location at a specific time and representatives for each candidate, if not a campaign staffer or candidate themselves, pitch their campaign in hopes of winning over their fellow caucusgoers -- a process that can involve lengthy discussions before ballots are cast.

The public nature of caucuses is what sets them apart from a typical primary where, like in normal elections, voters can arrive at a polling location at any time throughout the day (or vote early or by mail, depending on the state), privately cast their secret ballot and then leave.

What are delegates and why are candidates competing for them?

In politics, a delegate is a person who is elected to represent others at a political gathering. When it comes to the presidential primaries and caucuses, delegates are people from either party who are elected -- usually at separate caucuses or conventions -- by others from their party to represent the candidate they support at the party's national convention.

Presidential candidates are competing to get the most delegates because if they get a majority of them, they are guaranteed the presidential nomination.

A Republican candidate must earn at least 1,215 delegates to secure the nomination in 2024, according to the Republican National Committee; while a Democratic candidate must get 1,968 delegates, according to the Democratic National Committee.

When are candidates nominated and when are the party conventions?

Candidates are formally nominated as their party's nominee at their respective party's national convention, which is a massive gathering held every four years where members of the party gather to vote on their nominee, to plan for the upcoming election and traditionally mark the start of their nominee's general campaign.

The 2024 Republican National Convention will be held from Monday, July 15, through Thursday, July 18, in Milwaukee.

The 2024 Democratic National Convention will be held from Monday, Aug. 19, through Thursday, Aug. 22, in Chicago.

At both conventions, the delegates will formally vote on who they are supporting to become the presidential nominee and then separately vote on who they support for vice president.

This process is based on the results of the primaries and caucuses and presidential candidates typically pick a vice presidential candidate, who are then selected together.

During most years, because the primary and caucus results are public as they occur in real time, it's already known how many votes each presidential candidate will receive based on how many delegates they were allotted, although Democratic candidates are technically not bound to support the candidate they said they were pledged to.

Once the delegates vote on who should be the nominee, the winning presidential candidate becomes the party's nominee, and the nominees from each party begin campaigning for the general election against each other and angling to get votes from the public.

ABC News' Isabella Murray and Kendall Ross contributed to this report.