Packed with case examples, clinical tips, new and classic metaphors, reflection prompts, and learning exercises, this concise primer helps readers hone their skills and confidence for practicing acceptance and commitment therapy (ACT). Gjis Jansen is a leading ACT trainer and supervisor who explains complex concepts in a candid, conversational style. He offers a unique window into how ACT sessions unfold, equipping therapists to deepen their engagement with clients and select interventions that address clients' individual needs and struggles. This is the English edition of Het ACT basisboek, published in the Netherlands in 2023 and translated, updated, and revised by the author.