survey-based research on state politics demonstrates considerable change in the characteristics, attitudes, and party allegiances of state electorates and of change in state party organizations. A multivariate linear model of partisan competition is estimated dynamically using as predictor variables measures of change in the size, composition, and characteristics of state populations and measures of characteristics of state party systems. The resultant model explains approximately 80 percent of variation in change in partisan competition. It provides a portrait of contemporary state politics more consistent with that provided by research using survey data than those studies using existing aggregate data. Partisan competition has often been cast as a fundamental ingredient of democratic government. A classic exposition on the values of two-party competition is found in V.0. Key's Southern Politics in State and Nation (1949), in which the author argues that one-party southern politics aided in the development of issueless, faction-ridden, and often undemocratic state political systems (pp. 299-310). Competing parties, in Key's view, are important in a democratic system because the presence of serious opposition for control of the government promotes discipline within parties and leads parties to inject some issue content into campaigns for office. Without the discipline putatively linked to competition, the rational strategy for parties is to appeal to the median voter by avoiding issues that might only serve to alienate voters (see, e.g., Downs, 1957, pp. 27-33). Thus in one-party systems personalities and other attributes irrelevant to policy become the lifeblood of elections, giving rise to demagoguery, policy systems that consistently favor strong economic interests within a given state, and generally retarding the development of democratic institutions (Key, 1949, ch. 14). Key's discussion of the role of party competition provides the foundation for a large body of research in which partisan competition figures