Efforts to help young people have ancient historical roots, but "youth psychotherapy" has only been practiced for about a century and studied empirically for 50 years. Nonetheless, hundreds of randomized trials have now accumulated, and many specific treatments have sufficient empirical support that they are classified as evidence-based psychotherapies (EBPs). We examine the strength of that support, highlight specific EBPs for specific forms of youth dysfunction, and consider strategies for understanding how, with which groups, and under what conditions, the treatments produce beneficial effects. We also examine how specific these effects are (e.g., whether benefit is greatest for targeted symptoms), how robust (e.g., whether "blind" informants perceive benefit, whether effects vary with type of control group), and how effective when extended to youths in ethnic minority groups, low- and middle-income countries, war-torn regions, and the criminal justice and child protection systems. We discuss the challenge of disseminating EBPs and implementing them within the everyday practice of youth mental health care. Strategies for improving youth psychotherapies and intervention science are proposed, including making intervention research look more like clinical practice, leveraging the heuristic potential of usual clinical care, conducting more high-risk/high-gain research and finding ways to learn from treatment "failure," restructuring EBPs to fit clinical practice, boosting treatment effectiveness through monitoring and feedback, enriching our understanding of what makes treatments work, and building efficient and accessible delivery methods and models.