Over 80 percent of Spanish noblemen in the period between 1350 and 1750 chose their wives to be the guardians of their children and property, so women headed many of the most powerful noble families in Spain at regular intervals. To Spanish noblemen, the preservation of family, power, and lineage was more important than the prescriptive gender roles of their time, and they expected and trained their female relatives to take an active part in the economic and political affairs of the family. Drawing on noble wills, guardianship agreements, dowry contracts, and lawsuits, this study demonstrates that noblemen’s dependence on their female relatives created an inheritance system that was almost bilateral in its flexibility and beautifully adapted to conquer the challenges the nobility faced daily.