This toolkit begins with a discussion of how both data and collaboration are integral to a successful justice reinvestment approach. The first section describes the specific support needed from key stakeholders and participating agencies. The next section examines the basic steps of collecting and organizing relevant criminal justice data, including articulating key questions, identifying relevant data sources, and addressing barriers to the collection and sharing of information. Once a jurisdiction has collected relevant criminal justice data, it will need to analyze those data to identify and quantify criminal justice population and cost drivers. The next section focuses on the steps required to identify appropriate data, answer key questions about the characteristics and movements of the local criminal justice population, and quantify criminal justice system costs. Finally, the concluding two sections discuss translating population and cost drivers into policy options that have a greater impact on public safety, are less expensive, and/or resolve cases more efficiently. Figures, tables, notes, and appendix