This handbook examines advances in the evidence-based behavioral family intervention, parent-child interaction therapy (PCIT). It surveys innovative adaptations tailored to specific diagnostic concerns, client populations, treatment settings, and delivery formats. Chapters provide rationales for adaptation, reviews of relevant research, and discussions of advantages and challenges. Case studies illustrate the implementation of the adaptations and help to make new techniques concrete. The handbook offers practical descriptions of the adaptations to PCIT, comprehensively reviews treatment outcome literature, and integrates cutting-edge implementation science into an exploration of the current dissemination strategies in PCIT. The handbook concludes with a consideration of the questions that remain to be addressed to extend the reach of PCIT among traditionally underserved families and to continue to advance the science and practice of children's mental health interventions.