From January to June 2004, states across the nation will hold their first round of elections, either a primary or a caucus to nominate delegates who will represent their candidate at the national party convention.

Although the caucus was the original method for selecting candidates, it is now the least popular, with only 14 states and Washington, D.C., participating in them. The other 36 states hold primaries.

Although both select delegates, the process of the caucus and primary are radically different. The caucus requires voters to show up at polling locations where they will listen to speeches and debates sometimes lasting for hours. Voters participating in a primary must go to a polling place and cast a ballot.

Caucus
Iowa's well-known caucus marks the beginning of the primary season. As the first election of the primary season, candidates concentrate on gaining support in Iowa, creating a huge media buzz leading up to the vote, which in 2004 occurs on Jan. 19.

Participating in a caucus requires more time than a primary. In Iowa, caucus participants will gather in high schools, living rooms and town halls across the state, and citizens will deliver speeches on behalf of candidates. An informal vote count will then be taken.

From there, the process continues at the state level: at a statewide convention, Iowa's delegates are chosen for the national convention.

Such additional time commitment is the caucus's major drawback; consequently, there is less participation in caucuses than in primaries. The Iowa caucus will typically attract 100,000 participants.

The caucus, however, encourages more intense voter participation in the nominating process than does a primary.

Primary
Florida adopted the primary in 1904 as a way to choose delegates, and within a decade many states followed suit. But it was not until 1969, when -- in an attempt to increase citizen participation -- the McGovern-Fraser Commission evaluated the process used to select delegates, that the primary won the popularity it enjoys today.

The sweeping changes made to the system led many states to switch to the primary, because more citizens were able to make the choice for delegates, rather than the state officials who had traditionally voted.

In a primary, as in a caucus, voters elect delegates who support their candidate choice, but the vote is taken by ballot and the process is similar to a general election. New Hampshire hosts the nation's first primary, held in 2004 on Jan. 27. The New Hampshire primary typically attracts 300,000 voters.

State-to-State
Rules for primaries and caucuses vary by state. Each state party uses its own rules for delegate selection, but those rules are subject to approval from the Republican National Committee or the Democratic National Committee and the state's election law. Usually, the state's legislature decides on the date and format for the primary or caucus.

-- By Sheryl Silverman, Online NewsHour