This editorial begins with an historical review of U.S. juvenile justice system reforms that have been influenced by psychological science. We then use a T-phase lab-to-legal system model to classify translational psychological research relevant to juvenile justice and illustrate how translational developmental research is guiding reforms in this field. We conclude by describing how the articles in this Special Issue serve as examples of various points within the modified T-phase model and contribute to the ongoing role of psychological science as a driver of change within juvenile justice systems. (PsycINFO Database Record (c) 2019 APA, all rights reserved)