Many current approaches to the treatment of psychological problems focus on specific disorders and techniques that are purported to be effective and distinct. Recent advances in knowledge and theory, however, have called into question this approach. The conceptual framework of transdiagnostic, rather than disorder specific, processes is gaining traction. Alongside this has been the call to focus on evidence-based principles rather than evidence-based practices and techniques. The rationale behind this is that many apparently unique and innovative practices are usually the reflection of common underlying principles. This book describes three foundational principles that are key to understanding both the rise and the resolution of psychological distress. Principles-Based Counselling and Psychotherapy promotes a Method of Levels (MOL) approach to counselling and psychotherapy. Using clinical examples and vignettes to help practitioners implement a principles-based approach, this book describes three fundamental principles for effective therapeutic practice and their clinical implications. The first chapter of the book provides a rationale for the principles-based approach. The second chapter describes the three principles of control, conflict, and reorganisation and how they relate to each other from within a robust theory of physical and psychological functioning. The remainder of the book covers important aspects of psychological treatment such as the therapeutic relationship, appointment scheduling, and the change process from the application of these three principles. With important implications for all therapeutic approaches, Principles-Based Counselling and Psychotherapy will be an invaluable resource for psychotherapists, counsellors and clinical psychologists in practice and training. It provides clarity about their role, and a means for providing a resolution to psychological distress and improving the effectiveness of their practice.