Mental health-substance use is a complex interrelation, with equally complex implications for individuals and their families, health professionals and society. Although its international recognition as an issue of critical importance is growing, clear guidance for professionals on mental health-substance use and its treatment is hard to find. The Mental Health-Substance Use series has been written to address this need, concentrating on concerns, dilemmas and concepts that impact on the life and well-being of affected individuals and those close to them, and the future direction of practice, education, research, services, interventions, and treatment. This first book outlines the specific health issues, experiential aspects, treatment options and wider implications of mental health-substance use, as well as defining the field, through contributions from international experts and practitioners. This Introduction and the subsequent volumes will challenge concepts and stimulate debate, exploring all aspects of the development in treatment, intervention and care responses, and the adoption of research-led best practice. They are essential reading for mental health and substance use professionals, students and educators.