The risk-need-responsivity framework is based on a review of the empirical literature on offender factors that affect recidivism. The emphasis is on responsivity or the alignment of the risk and need profile with programs that are suitable to reduce recidivism. The empirical basis for the three-part framework is reviewed in this chapter with attention to integrating intervention science into a definition of responsivity. A review of the research literature since the original design of RNR (in the late 1980s) reveals that not all of the eight static and dynamic (criminogenic needs) risk components have a direct relationship with recidivism and that there are clinically relevant factors that need to be included when considering the effectiveness of an intervention, program, service, or control strategy. This chapter provides a different "sorting" of the risk and need factors besides the inclusion of gender and developmental (age) factors and clinically relevant factors (i.e., mental health status and substance abuse) that affect recidivism. The purpose is to lay the foundation for further chapters that describe the parameter and inputs into the RNR simulation model. This chapter illustrates the robustness of the original conceptual framework while demonstrating the elasticity to reframe the model based on new and emerging literature on factors that affect recidivism. Focusing attention on recidivism, and recent efforts to identify programmatic factors for different risk-need profiles, provides an opportunity to further refine the RNR model to be compatible with current research.