This policy brief is one of three publications designed to guide local policymakers in undertaking justice reinvestment, a data-driven strategy to identify the drivers of criminal justice system costs and make more efficient use of resources while maintaining public safety. This brief discusses the central role of strategic planning entities in the justice reinvestment process; outlines how these bodies are structured and operated; and provides guidance in establishing or expanding such a collaborative. A case study from one local justice reinvestment site is presented to highlight the recommended process. Additional resources and a "getting started" worksheet are included in an appendix.