This essay deals with rules and attitudes towards the Spanish succession crisis from 1580 to the extinction of the Spanish Habsburg dynasty in 1700. It argues that apart from succession laws, which were set down in the legal texts of the many different realms under Habsburg authority, attitudes and expectations created implicit rules for the succession. These attitudes and expectations have been distilled by analyzing testaments, representation of deceased relatives in the Escorial, and the behaviors toward royal children. This analysis shows that Spanish royal attitudes to the succession differed considerably from codified law, and the kings of Spain were primarily guided by the former. This essay demonstrates, therefore, that in order to understand the development of the Spanish succession crisis, the traditional focus on biology, politics, and laws should be expanded to include the dynasty’s implicit rules of succession.