We link the intensity of campaign competition in different electoral systems with the number of candidates running for public office and their ideological differentiation. We show that proportional elections have more candidates, competing less aggressively in campaign spending, than those in majoritarian elections. Candidates’ ideological positions, however, can in general be more differentiated in majoritarian or proportional elections. We also study the equilibrium effects of plurality premiums and the consequences of heterogeneity among candidates in non-ideological characteristics.