Primary elections in the United States

Primary elections in the United States are those elections in which the candidates for a particular office—federal, state, or local—are chosen by registered voters in a particular jurisdiction. After the preliminary primary election, a general election is held to fill the office with one of the candidates chosen in the primary election. The United States is one of few countries to select candidates through popular vote in a primary election system; most countries rely on party leaders to vet candidates, as was previously the case in the U.S.State law, not federal, regulates most aspects of primary elections, and local election officials (county, city, and township) are predominantly responsible for administering them.

Primary election (11 C.F.R. 100.2):

A primary election is an election which meets one of the following conditions:

In the United States, other types can be differentiated:

Primaries can be used in nonpartisan elections to reduce the set of candidates that go on to the general election (qualifying primary). (In the U.S., many city, county and school board elections are non-partisan.) Generally, if a candidate receives more than 50% of the vote in the primary, he or she is automatically elected, without having to run again in the general election. If no candidate receives a majority, twice as many candidates pass the primary as can win in the general election, so a single seat election primary would allow the top two primary candidates to participate in the general election following.

As a result of a federal court decision in Idaho Republican Party v. Ysursa, the 2011 Idaho Legislature passed House Bill 351 implementing a closed primary system.

Oregon was the first American state in which a binding primary election was conducted entirely via the internet. The election was held by the Independent Party of Oregon in July, 2010.

...
Wikipedia