ACT in Steps: A Transdiagnostic Manual for Learning Acceptance and Commitment Therapy by Michael P. Twohig, Michael E. Levin, and Clarissa W. Ong is a practical, step-by-step guide for therapists learning to apply Acceptance and Commitment Therapy across a wide range of psychological difficulties. The book introduces the foundations of ACT and guides clinicians through assessment, case conceptualization, treatment planning, and a structured sequence of therapy sessions. It covers creative hopelessness, acceptance, cognitive defusion, mindfulness, self-as-context, values, and committed action, while providing exercises, worksheets, homework activities, and client materials that can be used directly in practice. Rather than focusing on a single diagnosis, the manual presents ACT as a transdiagnostic approach for working with clients who struggle with difficult thoughts, emotions, and internal experiences. It is particularly useful for psychology and psychotherapy students, new therapists, and experienced clinicians who want a structured introduction to ACT practice.