Some states hold a caucus, rather than a primary election, to choose a delegate to send to the national party convention to select a presidential nominee. Generally, any voter registered with the party holding the caucus may attend. Voters gather in local meeting halls to discuss and debate the merits of the potential candidates and relevant issues. Voters then choose a delegate that they believe will represent the state's interests at the national party convention. Some states hold multiple caucuses before selecting a delegate for the national party convention.
Perhaps one of the most well known caucuses is the Iowa caucus. The Iowa caucus kicks off Presidential election season and is the first step in choosing Iowa's preferred partisan candidate for president.
Iowa has 1,774 voting precincts. Members of the those precincts gather in gymnasiums, high schools, church basements and other meeting places to hold a caucus. During the caucus, members of the precinct discuss and debate which delegate should represent their precinct at a later county convention. Representatives for candidates are also permitted to speak in an attempt to persuade undecided caucus voters.
Following the caucuses, at the county conventions, Democrats select delegates for a district convention. At the district convention, delegates are chosen for the state convention. Republicans choose their delegate for the state convention at the county convention.
It is not until the state conventions that delegates cast their votes for delegates to the national party conventions where Iowa's preferred presidential candidate for Democrats and Republicans will be chosen.