This book explores the development and implementation of Child First as an innovative guiding principle for improving youth justice systems. Applying contemporary research understandings of what leads to positive child outcomes and safer communities, Child First challenges traditional risk-led and stigmatising approaches to working with children in trouble. It has now been adopted as the four-point guiding principle for all policy and practice across the youth justice system in England and Wales, it is becoming a key reform principle for youth justice in Northern Ireland, and it is increasingly influential across several western jurisdictions. With contributions from academics, policymakers and practitioners, this book critically charts the progress and challenges in establishing a progressive evidence-led youth justice system. Its dynamic and accessible integration of theory, research, policy and practice, alongside discussion of critical themes, makes it a key read for students on youth crime/justice modules and for a wider market. Stephen Case is Professor of Youth Justice in the Criminology, Sociology and Social Policy division at Loughborough University, UK.  Neal Hazel is Professor of Criminology and Criminal Justice in the School of Health and Society at the University of Salford, UK.