Too few investigations have attempted to shore up critical knowledge gaps about post-Soviet states by conducting comparative analyses of political institutions and developing rigorous methods suitable for cross-national longitudinal analysis. This book attempts to close a few of the gaps left by many previous publications in the post-Soviet field. It conducts a cross-country multiple-election examination of political party systems in Estonia, Latvia, Lithuania, Russia, and Ukraine in the past one and a half decades. The project measures and explains different degrees and dynamics of party system institutionalization in these five nations -- an important factor bearing on the progress of a nation toward consolidating stable democracy.