Dr. Leah Somerville is the Grafstein Family Professor of Psychology at Harvard University, and my very own PhD advisor! She runs the Affective Neuroscience & Development Laboratory, where we study how brain and pubertal development shapes motivation, cognition, emotion, and behavior during adolescence. In this special 100th episode, I interview Leah in person about her research background, the importance of adolescence as a sensitive period for brain development, myths and facts about puberty, hormones, sex differences, and teenage risk-taking, and where developmental neuroscience fits into juvenile justice and our legal conceptions of rational agency.