In the summer of every presidential election year, political parties in the United States typically conduct national conventions to choose their presidential candidates. At the conventions, the presidential candidates are selected by groups of delegates from each state. After a series of speeches and demonstrations in support of each candidate, the delegates begin to vote, state-by-state, for the candidate of their choice. The first candidate to receive a preset majority number of delegate votes becomes the party's presidential candidate. The candidate selected to run for president then selects a vice presidential candidate.

Delegates to the national conventions are selected at the state level, according to rules and formulas determined by each political party's state committee. While these rules and formulas can change from state-to-state and from year-to-year, there remain two methods by which the states choose their delegates to the national conventions: the caucus and the primary.

The Primary

In states holding them, presidential primary elections are open to all registered voters. Just like in general elections, voting is done through a secret ballot. Voters may choose from among all registered candidates and write-ins are counted. There are two types of primaries, closed and open. In a closed primary, voters may vote only in the primary of the political party in which they registered. For example, a voter who registered as a Republican can only vote in the Republican primary. In an open primary, registered voters can vote in the primary of either party, but are allowed to vote in only one primary. Most states hold closed primaries.

Primary elections also vary in what names appear on their ballots. Most states hold presidential preference primaries, in which the actual presidential candidates' names appear on the ballot. In other states, only the names of convention delegates appear on the ballot. Delegates may state their support for a candidate or declare themselves to be uncommitted.

In some states, delegates are bound, or "pledged" to vote for the primary winner in voting at the national convention. In other states, some or all delegates are "unpledged," and free to vote for any candidate they wish at the convention.

The Caucus

Caucuses are simply meetings, open to all registered voters of the party, at which delegates to the party's national convention are selected. When the caucus begins, the voters in attendance divide themselves into groups according to the candidate they support. The undecided voters congregate into their own group and prepare to be "courted" by supporters of other candidates.

Voters in each group are then invited to give speeches supporting their candidate and trying to persuade others to join their group. At the end of the caucus, party organizers count the voters in each candidate's group and calculate how many delegates to the county convention each candidate has won.

As in the primaries, the caucus process can produce both pledged and unpledged convention delegates, depending on the party rules of the various states.

How Delegates are Awarded

The Democratic and Republican parties use different methods for determining how many delegates are awarded to, or "pledged" to vote for the various candidates at their national conventions.

Democrats use a proportional method. Each candidate is awarded a number of delegates in proportion to their support in the state caucuses or the number of primary votes they won.

For example, consider a state with 20 delegates at a democratic convention with three candidates. If candidate "A" received 70% of all caucus and primary votes, candidate "B" 20% and candidate "C" 10%, candidate "A" would get 14 delegates, candidate "B" would get 4 delegates and candidate "C" would get two delegates.

In the Republican Party, each state chooses either the proportional method or a "winner-take-all" method of awarding delegates. Under the winner-take-all method, the candidate getting the most votes from a state's caucus or primary gets all of that state's delegates at the national convention.

Key Point: The above are general rules. Primary and caucus rules and methods of convention delegate allocation differ from state-to-state and can be changed by party leadership. To find out the latest information, contact your state's Board of Elections.

Types of Delegates

Most of the delegates from each state are selected at the “district-level” to represent specific geographic areas, usually the state’s congressional districts. Other delegates are “at-large” delegates are chosen to represent the entire state. Within both the district-level and at-large delegates, there are other types of delegates whose obligations and duties vary according to the rules of their political party.

Democratic Party Pledged Delegates

From the 1980 Democratic National Convention in New York City. Allan Tannenbaum/Getty Images

Pledged delegates in the Democratic Party are required to express a preference for either one of the party’s presidential candidates or an uncommitted preference as a condition of their selection. Under current party rules, delegates pledged to a specific candidate are encouraged—but not required—to vote for the candidate they had been selected to support.

Democratic Party Unpledged Delegates

Unpledged delegates in the Democratic Party are not required to pledge their support to any of the party’s presidential candidates. Often called “superdelegates,” unpledged delegates include members of the Democratic National Committee, Democratic members of Congress, Democratic governors, or distinguished party leaders, including former presidents and vice presidents. They are free to support any of the presidential candidates.

Republican Party Automatic Delegates

Republican National Convention on July 21, 2016 at the Quicken Loans Arena in Cleveland, Ohio. John Moore/Getty Images

Three members of each state’s Republican National Committee are sent to the convention as automatic delegates, meaning they are exempt from the regular selection process. Automatic delegates make up about 7% of all delegate and are either “bound” to a particular candidate or “unbound.” Bound delegates are obligated to express support for particular candidate as determined their state’s primaries or caucuses. Unbound delegates are free to express support for any candidate, regardless of the caucus or primary results in their state.

Pledged Republican Delegates

In the Republican Party, pledged delegates may either be bound delegates or unbound delegates who have been pledged to a candidate "by personal statements or even state law, but according to RNC rules, may cast their vote for anyone at the convention,” according to the Congressional Research Service.

More About the Democrat’s Superdelegates

In the Democratic Party only, certain delegates to the Democratic National Convention are designated as “superdelegates” who selected automatically rather than through their states’ traditional primary or caucus systems. Unlike regular “pledged” delegates, the superdelegates are free to support and vote for any party candidate for the Democratic presidential nomination. As a result, they can effectively supersede the results of the Democrat Party primaries and caucuses. The superdelegates, who make up about 16% of all democratic convention delegates, include elected officials—like U.S. Representatives, Senators, and governors—and high-ranking party officials.

Since it was first used in 1982, the superdelegate system has been a source of controversy in the Democratic. This reached a boiling point during the 2012 campaign when several superdelegates publicly announced that they would support Hillary Clinton while the state primary elections were still being held. This angered supporter of Bernie Sanders, who felt party leaders were unfairly attempting to tip the scales of public opinion in favor of Clinton, the eventual nominee. As a result, the party has adopted new superdelegate rules. Beginning with the 2020 convention, the superdelegates will not be allowed to vote of the first ballot unless the outcome is not in doubt. In order to win the nomination on the first ballot, the leading candidate must win the votes of a majority of the regular pledged delegates awarded through the primaries and caucus leading up to the Democratic Convention.

To be clear, there are no superdelegates in the Republican Party nomination process. While there are Republican delegates who are automatically chosen to attend the party convention, they are limited to three per state, consisting of the state chairman and two district-level committee members. In addition, they are required to vote for the winner of their state’s primary election, just like the regular pledged delegates.