This chapter analyses the institutional architecture and political reforms of the Iberian monarchies from the sixteenth century to the end of the eighteenth century, underlining two main ideas. First, the persistence of an institutional model based upon jurisdictional autonomies until the end of the seventeenth century. This political framework was based on cooperation and negotiation allowing the participation of the different institutional and social bodies in the political decision-making process. Iberian monarchs and their ministers were able to establish alliances with local oligarchies, important noble houses, guilds and, of course, the Church. This system was partly disrupted by a movement of political reforms that reinforced State interventionism in the economy during the eighteenth century. Second, the limited economic impact of such reforms prevented an economic growth similar to other Western European territories. They faced resistance of the kingdoms and territories, which aimed to preserve their customs and the resistance of the privileged groups who struggle to maintain their properties and fiscal privileges. Both factors detained the attempts of centralizing reforms and undermined the process of increasing state capacity.