A City Region Food System (CRFS) approach to food system assessment offers concrete policy and capacity-building guidance to address complex sustainable development issues and to more directly link rural and urban areas and communities. In turn, improved CRFS may help achieve better economic, social, and environmental conditions in both urban and surrounding rural areas. This chapter describes the CRFS toolkit, which was derived from insights and lessons learned through seven pilot CRFS interventions. Elements of the toolkit include sections on how to define the boundaries of a CRFS, how to develop a local vision, how to characterize and conduct an analysis of a CRFS, and how to engage in policy and planning. The toolkit also suggests methodologies for engaging in governance and multi-stakeholder dialogue processes. The toolkit is connected to synthetic reports covering seven pilot cities globally, providing details about both the implementation and results of these CRFS interventions.