Probably the most well-known literature on electoral systems highlights how electoral rules shape the number of parties (see especially Cox 1997; Duverger 1954; Lijphart 1994; Taagepera and Shugart 1989). We, therefore, begin our analysis by exploring how different rules affect the number of parties, but we then turn to how political context – in the form of democratic experience and party institutionalization – conditions the effects of rules.

In this chapter, we lay out the concepts necessary to explore the relationship between electoral rules, context, and the number of parties. First, we discuss the principal expectations about how electoral rules affect disproportionality (i.e., the extent to which parties’ seat shares deviate from their share of the vote) and the number of parties. Second, we consider how democratic experience and party system development may condition these effects. Third, we explain how we measure the central variables – especially disproportionality, the effective number of parties, democratic experience, and party institutionalization. Finally, we discuss how specific institutional features of mixed-member systems might also shape the number of parties.

Cutting to the chase, and laying out our most important expectation, we expect restrictive electoral rules (especially FPTP) to be much less likely to constrain the number of parties in new democracies, especially those with poorly developed party systems, than in established democracies.