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 focuses on the tracking costs and anticipated savings to target reinvestment. It provides guidance on how to conduct a comprehensive assessment of local justice spending, assess cost implications for agencies outside the criminal justice system, and target reinvestment efforts. Additional resources and a "getting started" worksheet are included in an appendix.