This chapter starts with a description of Adler’s personal and family backgrounds, including growing up in the shadow of a high-achieving and popular older brother; life-threatening and disabling illnesses during his childhood; struggles to enter and complete his medical school education; dissatisfaction with academic medicine focusing on diseases instead of patients; his egalitarian medical practices; and his involvement in social and public health reform. It also includes narratives of Adler’s marriage with his Russian Jewish wife, who had strong socialist commitments, as well as their relationship with various communist revolutionaries. It then describes Adler’s association with Freud and their eventual separation, the evolution of Adler’s theories and practices, the differences in the temperament and orientations between Adler and Freud, and the continuing mutual influences between Adler and Freud even long after their break-up. It ends with a discussion of Adler’s role in and contribution to the field of psychotherapy and the mental health movement.