The concept of therapeutic mechanism occupies a contested and generative space across the depth-psychology corpus. The term designates the operative processes by which psychotherapeutic interventions produce change — a question that proves far from settled and that ramifies differently depending on whether one stands within the classical analytic tradition, transpersonal psychiatry, group dynamics, somatic approaches, or neurobiological research. Grof’s LSD investigations press the question to its outermost limits, arguing that mechanisms operative at biographical and perinatal levels are insufficient to explain certain clinical transformations, and that a distinct class of transpersonal mechanisms must be theorized. Yalom, by contrast, grounds the question firmly in the interpersonal field of the group, identifying cohesion, social learning, catharsis, and the corrective emotional experience as the demonstrable engines of change, while insisting that their interaction is multidimensional and irreducible to any single agent. Jung’s early writings locate mechanism in the abreaction-transference nexus, noting that abreaction alone is insufficient. Levine, Ogden, and van der Kolk redirect attention to somatic and neurological substrates — the body as both repository and vehicle of therapeutic action. The Wampold line of inquiry foregrounds common factors and the real relationship as mechanism-candidates transcending specific techniques. What unites these voices is a shared recognition that the question of mechanism is not merely technical but epistemological: how one theorizes what heals determines what one looks for, and what one misses.