Motivational Interviewing (MI), as represented in the depth-psychology corpus, is above all the intellectual project of William R. Miller and Stephen Rollnick — a clinical method refined across three editions into a coherent theoretical and practical system for facilitating human change. The corpus treats MI not as a technique but as a relational spirit: a guiding orientation built upon accurate empathy, collaborative partnership, and the elicitation of intrinsic motivation rather than its imposition. Miller’s third edition constitutes the primary documentary anchor, establishing MI’s four-process architecture (engaging, focusing, evoking, planning), its signature OARS skill set, and its conceptual vocabulary of change talk, sustain talk, equipoise, and the righting reflex. The corpus reveals MI’s remarkable diffusion across clinical populations — substance abuse, eating disorders, criminal justice, adolescent health, psychiatric comorbidity — while simultaneously foregrounding unresolved tensions: the ethics of directed influence, the conditions under which MI proves harmful for change-ready clients, the persistent challenge of fidelity and training, and the question of how much flexibility therapist manuals should permit. The psycholinguistic turn — tracking commitment language as outcome predictor — marks the most theoretically ambitious development within the tradition. MI thus sits at the intersection of humanistic psychology, behavior change science, and clinical pragmatism.