All U.S. states and territories use primary elections to select party nominees for at least some offices. Primaries are the latest development in a decades-long trend toward including more people in party nomination processes, and have largely replaced caucuses and conventions, though these are still used in some circumstances.
This toolkit highlights how state primaries differ. The links lead to webpages that explain each resource in detail. In brief:
- State primary election types: This page covers NCSL’s taxonomy for categorizing primaries: closed, partially closed, open to unaffiliated, partially open, and open. It also covers newer systems like California and Washington’s top-two, Alaska’s top-four and Louisiana’s all-comers system (sometimes referred to as a “jungle primary”).
- Changes to state primary elections since 2000: This page covers all changes to state primary types since 2000. It also sheds light on primary types used in the past that have been declared unconstitutional by courts.
- How states differentiate presidential primaries from state primaries: This page covers which states use different primary types for state primaries and presidential primaries. In some cases, the distinction is necessary because the state runs a unique primary type for state offices it chooses not to apply to the presidency.
- Primary runoffs: This page covers the runoff processes some—mostly southern—states use to ensure party nominees receive a certain percentage of votes. In many cases the necessary level of support is a majority, but some states use different thresholds. In states that require a certain threshold, if it is not met, a primary runoff is held shortly thereafter.
- Primary election turnout in midterms since 2000: This page covers the how turnout has fluctuated in the four most recent midterm elections (2010, 2014, 2018, 2022). There are three tables: overall turnout, the difference in turnout between primaries and runoffs where applicable, and turnout across these years by primary type. Data for these tables comes from the Bipartisan Policy Center.
- Voting age for primary elections: This page covers which states permit people under the age of 18 to participate in primary elections, as long as they will be 18 by the general election.
- Primaries: more than one way to find a party nominee: This report from 2021 addresses the history of primaries, the legal landscape, political and administrative features of various primary types.
- Requirements to run for legislative office: This page covers the requirement to run for legislatures in all 50 states, the District of Columbia and Puerto Rico. While not directly related to the mechanics of primaries, its resources complement the toolkit by showing how candidates can put their name in the hat for elective office.
NCSL thanks Unite America for supporting our primaries research.