Each year, in more than a billion U.S. medical visits, health professionals offer disease prevention and treatment recommendations, but close to half of these are not followed. This book provides the latest theory-driven and evidence-based recommendations for addressing persistent barriers to treatment adherence within a social-ecological framework. Written for a wide variety of practitioners, the numerous cases and clinical examples illustrate important practice principles. Each chapter includes tools for instruction and self-study (including learning objectives, a summary, review questions, prompts for discussion and further study, and suggested reading), making it an ideal text for clinical health-science courses. With a strong evidence base and a readable style, this book is for practitioners and students in medicine, public health, nursing, health education, health coaching, allied health, dentistry, clinical and health psychology, counselling, and social work. It is also for anyone who wishes to take an active role in their own health or help others to do so.