Definition

Open primary definition

Last updated: November 2026

An open primary is a primary election in which a registered voter may vote in any one party's primary without being a registered member of that party.

The voter chooses a party ballot at the polls or by mail, votes in only one party contest, and keeps the same registration afterward. Twenty states use fully open primaries in 2026.

What is the open primary definition in AP Gov?

In AP U.S. Government, an open primary is a primary in which voters decide on election day which party's primary to vote in, without declaring party membership in advance. Textbooks pair it with the closed primary, where only registered party members vote, and the blanket primary, where every candidate shares one ballot.

For an exam answer, the key contrast with a closed primary is simple: an open primary has no membership requirement. The key contrast with a blanket or top-two primary is that you still pick one party's ballot.

Definition

Open primary (government definition)

Open primary: a party nominating election in which any qualified, registered voter may participate in the primary of one party of their choosing, regardless of their own party registration or lack of one. The voter receives only that party's ballot and cannot vote in a second party's primary in the same election. 20 states use this system in 2026: Alabama, Arkansas, Georgia, Hawaii, Illinois, Indiana, Michigan, Minnesota, Mississippi, Missouri, Montana, New Mexico, North Dakota, Ohio, South Carolina, Tennessee, Texas, Vermont, Virginia, and Wisconsin.

Variant

Semi-open primary definition

A semi-open primary lets any voter request any party ballot, but the choice may be recorded publicly or treated as affiliating with that party. Arizona, Colorado, and Maine are classified as semi-open in 2026. Independents can still vote; their choice simply may show up in the voter file.

Variant

Semi-closed primary definition

A semi-closed primary admits registered party members plus unaffiliated voters, but blocks members of other parties from crossing over. District of Columbia, Idaho, Massachusetts, Nebraska, New Hampshire, North Carolina, Oklahoma, Rhode Island, Utah, and West Virginia use semi-closed primaries in 2026.

Opposite

Closed primary definition

A closed primary limits each party primary to that party's registered members. Independents get no ballot unless they join a party before the state deadline. Fifteen states use closed primaries in 2026, including New York, Florida, and Pennsylvania.

Beyond party primaries

Top-two and top-four primary definition

A top-two primary puts every candidate on one ballot for every voter, and the two highest finishers advance regardless of party. California and Washington use it. Alaska's top-four primary advances four candidates to a ranked-choice general election. See which states have top-two primaries.

Open vs closed primary definition, side by side

Every primary definition comes down to who may vote and whether you must join a party first.

Open Primary Guide: the six U.S. primary types in 2026, from most open to least open.
Primary type	Who can vote	Must join a party?	Independents	States (2026)
Top-Two	Every registered voter	No	Same single ballot as everyone	2
Top-Four	Every registered voter	No	Same single ballot as everyone	1
Open	Any registered voter	No	Vote in any one party primary	20
Semi-Open	Any registered voter	No, but the ballot choice may be recorded	Request any party ballot	3
Semi-Closed	Party members plus unaffiliated voters	Only if registered with another party	Pick one party ballot	10
Closed	Registered party members only	Yes, before the deadline	No primary ballot	15

Is an open primary the same as a blanket primary?

No. In a blanket primary, all candidates from all parties share one ballot and voters can pick across party lines race by race. The U.S. Supreme Court struck down California's partisan blanket primary in California Democratic Party v. Jones (2000), finding it burdened the parties' freedom of association.

The nonpartisan top-two primary followed. Because it does not pick party nominees at all, the Court upheld Washington's version in Washington State Grange v. Washington State Republican Party (2008). That history explains why some definitions you find online lump these systems together, and why they are legally distinct.

Common misunderstandings about open primaries

You cannot vote in two party primaries in one election, even in an open state.
Choosing a party ballot in a fully open state does not register you with that party.
The votes you cast stay secret in every state. Only the ballot type may be recorded, and only in some states.
Rules can differ for presidential primaries. Alaska, for example, uses top-four for state races but a closed presidential primary.

For a deeper reference on how states write these laws, the National Conference of State Legislatures keeps a summary of state primary types.

Keep reading

Start with open primaries

The first step is supporting open primaries for every voter. Next, see how More Choice Voting builds on them.

Support open primaries

Common questions

See all 44 answers

How do you define open primaries in one sentence?

An open primary is a party primary in which voters do not have to be registered members of the party to take part. The voter still picks only one party ballot per election. That single feature, no membership requirement, is what separates an open primary from a closed one.

What is the open primary definition in AP Gov?

In AP U.S. Government, an open primary is a primary election in which voters may choose on election day which party primary to vote in, without declaring party membership in advance. It is usually taught next to the closed primary, where only registered party members may vote, and the blanket or top-two primary, where every candidate shares one ballot.

What is a semi-open primary?

A semi-open primary lets any voter request any party ballot, but the choice may be recorded publicly or treated as a party affiliation. Arizona, Colorado, and Maine are classified as semi-open for 2026. The practical difference from a fully open primary is that your ballot choice can show up in the public voter record.

What is a semi-closed primary?

A semi-closed primary lets unaffiliated voters pick one party ballot while blocking voters registered with a different party from crossing over. Nine states plus Washington, D.C. use semi-closed rules in 2026, including Massachusetts, New Hampshire, North Carolina, and Utah. Some states record the unaffiliated voter as joining the party they chose.

What is a closed primary?

A closed primary limits each party primary to voters already registered with that party, so independents receive no primary ballot. Fifteen states use closed primaries in 2026, including New York, Florida, Pennsylvania, and New Jersey. Most closed states also set a deadline, sometimes months before the primary, for joining or switching parties.

What is a nonpartisan primary?

A nonpartisan primary puts every candidate on one ballot and lets every registered voter take part, regardless of party. The top finishers advance to the general election even if they share a party. California and Washington advance the top two. Alaska advances the top four to a ranked-choice general election.

Is an open primary the same as a blanket primary?

No. In an open primary you pick one party ballot. In a blanket primary every candidate is on one ballot. The U.S. Supreme Court struck down California's partisan blanket primary in California Democratic Party v. Jones (2000), then upheld Washington's top-two primary in Washington State Grange v. Washington State Republican Party (2008).