Party system

A party system is the durable pattern of competition and cooperation among political parties in a country or political arena. It shapes how parties win office, form governments, and represent social interests.

Political party: An organized group that seeks political power by contesting elections and coordinating government. Parties are the actors whose competition and cooperation make up a party system.
Duverger's law: A proposition linking plurality electoral rules to two-party competition and proportional rules to multiparty competition. It explains how electoral rules can encourage particular party-system patterns.
Two-party system: A party system in which two parties dominate electoral competition and government formation. It is a concentrated pattern of competition within the broader category.
Cleavage theory: An account of party systems as shaped by enduring social divisions that organize political conflict. It links party formation and persistence to social divisions.
Government formation: The process through which political actors assemble an executive government after an election or political transition. The number and bargaining power of parties shape who can form a government.
Electoral system: The rules that translate votes into elected offices. Electoral rules shape how many parties can compete effectively and win representation.
Proportional representation: An electoral system that allocates seats in rough proportion to parties’ vote shares. It often lowers barriers to representation for smaller parties.
Multiparty system: A party system in which more than two parties have meaningful electoral or governing influence. It contrasts with systems where two parties dominate.
Lipset–Rokkan model: A theory that explains European party systems through historical social cleavages and their institutionalization. It traces how conflicts such as center–periphery and class became party alignments.
Political accountability: The ability to hold public officials answerable for their decisions and conduct. Party competition can clarify responsibility for government performance—or diffuse it among partners.

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