Abstract: Mixed-member electoral systems are described as a mixture of two principles of electoral system design: majoritarian systems, which usually have single-seat districts with plurality rule and tend to give greater representation to the two parties that receive the most votes; and proportional systems, which have multi-seat districts, usually with party lists, and typically produce parliamentary representation that largely mirrors the vote shares of multiple parties. In the prototype mixed-member system, half the seats in a legislative chamber (the nominal tier) are elected in single-seat districts and the other half (the list tier) are elected from party lists allocated by proportional representation; such systems come in a wide variety of options, with the most important choices involved being those of how seats and/or votes are linked between the two tiers. Defines mixed-member electoral systems as a subset of the broader category of multiple-tier electoral systems. The typology of systems outlined is arranged in three main sections: Mixed-Member Systems as Variants of Multiple-Tier Electoral Systems; Majoritarian or Proportional: Linkage Between Nominal and Tier Lists—mixed-member majoritarian (MMM) and mixed-member proportional (MMP) systems; and How MMM and MMP Systems Work: Simple Systems and Additional Variables—this section includes a table of mixed-member systems in use around the world in 1999.

Keywords: electoral systems, list tier, mixed-member electoral systems, mixed-member majoritarian systems, mixed-member proportional systems, multiple-tier electoral systems, multi-seat districts, nominal tier, parliamentary representation, party lists, party representation, plurality rule, proportional representation, single-seat districts,