Before pharmaceutical products are evaluated in humans, it is essential that they undergo a rigorous safety assessment using in vitro models and studies in preclinical species. Once products progress into the clinic, additional preclinical studies are needed to support further clinical testing. Although regulatory guidelines provide a good framework for the types of studies that should be performed, there are some areas where it is unclear how these should be applied to microbicides, what study designs should be used, whether certain tests are relevant or if additional assays are appropriate. In this chapter we provide an overview of the key issues for the preclinical development of microbicides, and describe the purpose of each of the tests along with the key considerations to be taken into account when designing the individual safety studies as well as the overall preclinical program.