Work with young people on issues of substance misuse has for too long been based on adult-oriented research and adapted from adult-focussed practice. Introducing and assessing the evidence base that is being developed around work with children and young people, Youthoria provides startling and compelling conclusions that revise not only our understanding of problematic young substance users, but also of young people in all contexts of need. It: A A explains how young peopleA fs problematic substance use is not a random occurrence, but is entwined in adolescent development itself A A offers new directions in which to assess young people, in ways that are truly developmentally informed, so as to implement effective prevention and treatment efforts. Youthoria will help anyone working with young people and families, not only to develop a framework for learning and practice that makes sense of the complexity of young peopleA fs needs...but to do so in ways which make sense to young people too. It: A A offers guided access to an extraordinarily wide range of published research, evidence and practice wisdom - unprecedented in a single volume, accessible to specialists and generalists alike A A integrates multidisciplinary research from sociology, history, family studies, addiction and adolescent mental health research into a single framework for understanding young peopleA fs needs A A describes the key factors, causes, influences and evolution of use and misuse, in ways that support effective assessment and intervention planning A A provides insights from research into which young people are most prone to substance misuse, and their divergent responses to prevention and treatment A A describes both effective and ineffective prevention strategies, and considers why the formerA fs promising outcomes are not recognised A A explores the evidence base for what interventions work best for which young people and how best to measure this A A offers a clear framework for the implementation of a developmentally informed adolescent treatment system. A stimulating challenge to academics and practitioners alike, it will help them: A A increase their knowledge and range of skills to support young people and their families, across the full spectrum of their needs A A map the complexity of young peopleA fs substance use to ensure that those who need it receive optimal support A A improve outcomes especially while working with the most vulnerable, marginalised and excluded of young people.