The central argument of the chapter is that the enduring politicization of youth justice undermines research-informed policy and practice. The author first presents a brief overview of criminology and youth, which notes that a focus on youth and youth justice is deeply embedded within and across criminology through multiple realist, radical, critical and cultural perspectives. More recently, the "new penology" emphasizes risk management, assessment, and evaluation research. This overview is followed by a discussion of the application of criminological knowledge to research-informed policy and practice. It concludes that the combination of criminological knowledge, practice experience, and core human rights instruments provide a robust knowledge base that can be summarized in five core principles. One principle is that policy and practice should comprehensively address the social and economic conditions that are known to spawn social antagonism, distress, economic disadvantage, and criminal behavior. A second, closely related principle is that of "universality." This means that positive youth development requires holistic services that promote the rights, meet the needs, and safeguard the well-being of all children and youth. A third principle is that whenever possible, children and youth should be diverted from the formal youth justice system. The fourth principle emphasizes deinstitutionalization or "decarceration," since incarceration promotes a youth's becoming even more marginalized from mainstream socioeconomic opportunities. The fifth principle is that research-informed youth justice must resist the politicization of youth justice that emphasizes headline-grabbing "tough-on-crime" approaches to youth crime. Politicization ultimately eclipses, obscures, and corrupts knowledge derived from research and objectively tested practice. Responsible policymakers must base their decisions on research-based knowledge and practice rather than shifting subjective and selective assessments of public moods. 56 references