Book excerpt: This book provides an overview of the core research and theory on polyvictimization – exposure to multiple types of victimization that may have negative and potentially lifelong biopsychosocial impacts. The contributors to the volume address such topics as measurement issues in how polyvictimization should be assessed and measured; developmental risks of early childhood polyvictimization for maltreated children in foster care; gender differences in polyvictimization and its consequences among juvenile justice-involved youth; the importance of trauma-focused treatment for polyvictimized youth in the juvenile justice system; and the nature of polyvictimization in the internet era. Suited to readers who are new to the topic including graduate and undergraduate students, as well as researchers and clinicians who want a concise update on the latest empirical research from the frontiers of this field, this book provides findings and methodological innovations of interest to researchers and human service professionals. This book was originally published as a special issue of the Journal of Trauma & Dissociation.