Data can motivate and inform the development of juvenile justice reform efforts. Data are also essential for understanding the potential influence of reform activities, learning about what is working well, identifying racial and ethnic disparities, and strengthening policy and practice. In this brief, we describe how jurisdictions involved in a juvenile justice reform effort identified and addressed their data needs and incorporated data into their activities and decisionmaking. The information is based on a developmental evaluation of the Annie E. Casey Foundation’s expansion of the Juvenile Detention Alternatives Initiative® to the deep end of the JJ system. Deep-end reform aims to safely and significantly reduce the use of out-of-home placements for youth, especially youth of color. This brief supplements the information presented Keeping Youth Out of the Deep End of the Justice System: A Developmental Evaluation Overview of the Annie E. Casey Foundation’s Deep-End Reform, which provides an overview of the evaluation of the deep-end reform and its findings (appendix A provides details about the methods used in the evaluation).