The 21st century is placing new demands on toxicology, such as the need to evaluate many more chemicals than ever before, and to make toxicity testing more relevant to human exposure. Concomitantly, advances in molecular biology, systems biology, and computational methods are available to address these new needs. As a result, toxicology finds itself in a major transformational period represented by a shift from an observational science to one that is more predictive. The intent of this chapter is to review the enormously wide range of computational and biological assay platforms that are available for use in constructing a predictive toxicology program. These assay platforms all have their own strengths and weaknesses that need to be carefully considered. We conclude with a discussion of potential applications of these assay platforms.