Eligibility criteria for participation in mental health jail diversion programs often specify that, to be diverted, a candidate must not pose a level of threat to public safety that cannot be managed in the community. Risk assessment tools were developed to increase consistency and accuracy in estimates of threat to public safety. Consequently, risk assessment tools are being used in many jurisdictions to inform decisions regarding an individual's appropriateness and eligibility for mental health jail diversion and the strategies that may be successful in mitigating risk in this context. However, their use is not without controversy. Questions have been raised regarding the validity and equity of their estimates, as well as the impact of their use on criminal justice outcomes. The purpose of this review is to provide an overview of the science and practice of risk assessment to inform decisions and case planning in the context of mental health jail diversion programs. Our specific aims include: (1) to describe the process and components of risk assessment, including differentiating between different approaches to risk assessment, and (2) to consider the use of risk assessment tools in mental health jail diversion programs. We anchor this review in relevant theory and extant research, noting current controversies or debates and areas for future research. Overall, there is strong theoretical justification and empirical evidence from other criminal justice contexts; however, the body of research on the use of risk assessment tools in mental health jail diversion programs, although promising, is relatively nascent.