The theory of mentalizing and epistemic trust introduced by Peter Fonagy and colleagues at the Anna Freud Centre has been an important perspective on mental health and illness. This book is the first comprehensive account and evaluation of this perspective. The book explores 20 primary concepts that organize the contributions of Fonagy and colleagues: adaptation, aggression, the alien self, culture, disorganized attachment, epistemic trust, hypermentalizing, reflective function, the p-factor, pretend mode, the primary unconscious, psychic equivalence, mental illness, mentalizing, mentalization-based therapy, non-mentalizing, the self, sexuality, the social environment, and teleological mode. The biographical and social context of the development of these ideas is examined. The book also specifies the current strengths and limitations of the theory of mentalizing and epistemic trust, with attention to the implications for both clinicians and researchers.