Phrenology - a now dismissed and discredited science - was a popular but contested knowledge system in the nineteenth century. Its promoters touted its benefits, claiming that measuring and analyzing protrusions on the skull could solve life's most vexing personal questions: Who am I? Who should I marry? How should I raise my children? How do I treat my illness? How do I comprehend death? Delving into a rich archive of written and material sources, Carla Bittel uncovers the letters, diaries, marginalia, personal artifacts, and mapped heads which show phrenology was not merely directive but also interactive. Bittel argues that everyday users perpetuated phrenology as they adopted, adapted, and resisted it in their pursuit of self-knowledge. She examines how users tried to naturalize individual traits and generalize about the mental and physical qualities attributed to sex and race, revealing disconcerting implications for our modern fixation with knowing and improving ourselves.