This article uses a new institutionalist perspective to analyze how Mexico's constitutional system influences the country's party politics. Specifically, it argues that the centralization of power in the presidency and the prohibition of reelection of elected officials are two crucial features in Mexico's constitution that have important influences on party system development, the law-making process, and executive-legislative relations. Before the party turnover in 2000, these two constitutional features helped strengthen the party-state of the Institutional Revolutionary Party (PRI). However, since 2000 the two constitutional features have worsened executive-legislative relations under divided government, which in turn has reduced the quality of political representation and political accountability.