The emergence of competitive party politics in the countries of postcommunist Eastern Europe and the former Soviet Union has offered a unique opportunity to test some long-held propositions in party organization theory. What factors may promote certain types of organizations over others? To address this question, I develop a theoretical framework which identifies a set of party organizational types and the factors which might lead to the development of certain types over others. Second, I test these in light of the evidence from the communist successor parties from ten Eastem European and former Soviet countries. It was found that, among several independent variables, the previous communist regime type, the strength of the constitutional presidency, and the features of the electoral system were the best predictors of party organizational type among the communist successor parties.