A state-level election held before a general election to nominate a party's candidate for office.

Primaries are held for both the presidential and congressional races, although the exact regulations governing them and the dates on which they are held vary from state to state. In some states voters are restricted to choosing candidates only from the party for which they have registered support.

However 29 states permit "open primaries" in which a voter may opt to back a candidate regardless of their nominal affiliation.