Within the depth-psychology corpus, ‘therapeutic factors’ designates the elemental mechanisms through which group psychotherapy produces lasting change — a framework developed most systematically by Irvin Yalom and elaborated across decades of empirical and clinical inquiry. Yalom’s canonical taxonomy identifies eleven primary factors, ranging from instillation of hope and universality through altruism, imitative behavior, and group cohesiveness, to the apex triad of catharsis, self-understanding, and interpersonal learning. The research record, now spanning four decades of Q-sort studies and population-specific investigations, demonstrates both striking cross-population consensus and instructive variation: inpatient, geriatric, oncological, and offender populations each weight the factors differently, revealing that therapeutic factors are not fixed universals but context-sensitive levers. The here-and-now — the sustained focus on immediate intragroup experience — functions as the generative substrate from which several factors simultaneously emerge; it is, in Yalom’s formulation, the ‘power cell’ of group therapy. The social microcosm concept operates as the theoretical hinge, explaining how the group replicates each member’s relational world and thereby renders interpersonal pathology visible, workable, and ultimately correctable. Tensions persist between client-ranked and therapist-ranked hierarchies of importance, between efficiency-driven managed-care models and the interpersonally rich process Yalom defends, and between symptom-focused brevity and the full therapeutic harvest of process-illuminating work.