Drug development is a lengthy, multi-step process designed to characterize the safety and efficacy of drug candidates before being approved for marketing. Progression through the range of clinical trials and ultimately to product approval depends on a series of risk vs. benefit analyses. Risk is addressed, in part, through non-clinical safety assessment. Of particular importance are studies of safety pharmacology, general toxicology, genetic toxicology, carcinogenicity, and developmental and reproductive toxicology. While regulatory guidances and guidelines are available to provide recommendations related to non-clinical drug development, decision making must always be based on the best available science. This chapter covers the various types of non-clinical evaluations focusing on the overall goal of the studies, sources of regulatory recommendations, timing of submission, and utility of the data. Additional details are provided to familiarize the reader with various aspects of regulatory decision making.