This article recently published in Transcultural Psychiatry examines Fischl Schneersohn’s (1887–1958) “science of man” as a psychotherapeutic approach situated between modern psychology and Chassidic mysticism. While almost forgotten today, Schneersohn was a prolific writer, well-known in Yiddish-speaking circles as a psychologist, educationalist, novelist, and psychotherapist. As a descendant of an important dynasty of Chassidic rebbes, he grew up inside the Chabad movement, but followed a secular career. The first part of this article traces Schneersohn’s biography from the outskirts of the Russian empire to Germany, Poland, the United States, and Palestine, and shows how his upbringing and historical experiences shaped his psychological works and his self-understanding as educationalist and psychotherapist. The second part examines Schneersohn’s main work, Studies in Psycho-Expedition, which blended Chassidic mysticism and contemporary psychology in a way that was both idiosyncratic and unique. The psycho-sociological “science of man” was a modern psychological and psychotherapeutic approach, using specific methods to gain knowledge about the human mind, and to counteract and treat mental disorders, neuroses, and nervousness. At the same time, however, it was deeply influenced by Chassidic mysticism; revolving around the assumption of a universal human need for spiritual ecstasy. Schneersohn universalised, secularised, and reframed elements of the Kabbalah as a modern psychotherapy. By examining an almost forgotten psychotherapeutic approach outside the mainstream in its specific historical context, this article contributes to the history of the connection between religion and the psy-disciplines, as well as to ongoing debates about the role of spirituality and ecstasy in psychology and psychotherapy.