This dissertation explains how presidents achieved market-oriented reforms in a contentious political environment. The study focuses on Ecuador as a case study, where entrenched regional and ethnic divisions combined with lenient electoral institutions contributed to severe legislative fragmentation and pervasive executive-legislative conflict. Despite the adverse institutional context, presidents were able to assemble significant policy changes in congress without exclusively relying on constitutional decree authority. Patterns of policy change are explained by focusing on strategic actions adopted by political actors operating in a restrictive institutional framework. The dissertation develops a dynamic choice model to explain how coalition formateurs enhanced cooperation incentives by expanding the value of coalition benefits channeled through party leaders, and by lowering their partners' liability for making government coalitions. When presidents increased their cooperation incentives, party leaders acting as political brokers played a crucial role in producing disciplined majorities by allocating and rewarding party members with policy concessions, pork, and patronage. Elevated party unity scores and low defection rates suggest that individual vote buying was a strategy less preferred by presidents than commonly thought. Lowering the liability of coalition parties was crucial because public opinion ratings and the proximity of new elections reduced the incentives to cooperate with the executive. Crafting clandestine or 'ghost' coalitions compensated for high cooperation costs while allowing opposition parties to maintain a public image of political independence. Abundant quantitative and qualitative evidence, much of which is reported for the first time, provides empirical tests of model predictions. These data include legislative productivity rates, roll call votes, cabinet composition, legislative career paths, public opinion surveys, as well as insights from congressional hearings, media archives, and dozens of interviews with policy makers in Ecuador.