The article undertakes a comparative analysis of party systems concentrating on the evolution of parties and party systems since the World War II and particularly in the last decades of the XX century following drastic redefinition of political regimes; it also analyzes modern trends in development of parties in countries that either underwent democratization or ended up with political regimes in which one or more parties operate. The comparison is based on a set of quantitative criteria evaluating the efficiency of party system. Outlined are three scenarios; for each scenario analyzed are functions of political parties and trends of its evolution. The first scenario is tentative limitation of political pluralism; the second is “linear” development of multiparty systems; and the third is long-term period of limited competition in party space.