Primary elections (or primaries) are preliminary votes that determine which candidates will appear on the general election ballot, typically divided into open primaries (open to all voters) and closed primaries (restricted to registered party members). Rooted in the U.S. Progressive Movement, primaries were designed to shift candidate-nomination power from party leaders to the public, though parties still often use caucuses or conventions instead. In parliamentary systems, leadership elections often act as de facto prime ministerial primaries, as seen in Hungary's 2021 opposition primary or Portugal's 2014 Socialist Party selection. In the U.S., closed primaries are required in thirteen states as of 2026, with several others using them voluntarily or only for certain parties, while semi-closed systems also allow unaffiliated voters to participate. These primaries closely resemble the first round of a two-round (runoff) electoral system, sometimes called a "nonpartisan primary," and similar mechanisms appear in open-list proportional representation systems.