Closed primary

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. In modern politics, primary elections have been described as a significant vehicle for taking decision-making from political insiders to the voters, though this is disputed by select political science research. The selection of candidates for federal, state, and local general elections takes place in primary elections organized by the public administration for the general voting public to participate in for the purpose of nominating the respective parties' official candidates; state voters start the electoral process for governors and legislators through the primary process, as well as for many local officials from city councilors to county commissioners. The candidate who moves from the primary to be successful in the general election takes public office.

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.

When a qualifying primary is applied to a partisan election, it becomes what is generally known as a blanket or Louisiana primary: typically, if no candidate wins a majority in the primary, the two candidates receiving the highest pluralities, regardless of party affiliation, go on to a general election that is in effect a run-off. This often has the effect of eliminating minor parties from the general election, and frequently the general election becomes a single-party election. Unlike a plurality voting system, a run-off system meets the Condorcet loser criterion in that the candidate that ultimately wins would not have been beaten in a two-way race with every one of the other candidates.

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