Louis Sander’s cutting-edge approach drew on infant observation research; nonlinear dynamic systems theories; and current biology, physics, and other hard sciences. From this vantage point, he rethought the psychoanalytic approach to psychic structure, motivation, and therapeutic action. He opened a window for a broad and inclusive relational metapsychology of the highest order, updating Freud’s project of linking psychoanalysis with scientific paradigms. Sander emphasized the dynamic relationships between elements in systems, innovating in both method and content. This article offers an account of Sander’s broad and deep integration of psychoanalysis and developmental research.