摘要：Despite its high degree of institutionalization and the relative stability of electoral competition, the Uruguayan party system has undergone a significant transformation in the last forty years. This article analyzes that change, from the bipartisan equilibrium that remained until the 1960’s, to the new three party system equilibrium expressed in the 2009 elections results. To achieve that goal it examines the evolution of electoral results, electoral volatility, and party fragmentation, as well as the change of rules that allowed the consolidation of the new party system. This perspective helps to understand, from an institutionalist view point, the way in which highly institutionalized party systems change. The central hypothesis states that changes in party systems, originated by exogenous shocks, are processed gradually through changes in electoral rules that help to stabilize the system in a new equilibrium.
关键词：Party Systems;Institutionalization;Electoral Systems;Equilibrium;Uruguay.;Sistemas de Partidos;Institucionalización;Sistema Electoral;Equilíbrio;Uruguay.
