This chapter describes the use of various in silico, or computational, tools for the prediction of toxicity. The tools include those that are freely available as well as commercial software. There are a variety of in silico approaches to predict toxicity. Tools developed from structure–activity relationships (SARs) or structural alerts and quantitative structure–activity relationships (QSARs) are described. In addition, this chapter reviews the more recent advances in areas such as category formation to allow for read-across, as well as the development of databases of individual QSARs. Lastly this area is put in the context of tools to allow for the creation of computational workflows so that users can create and store their own in silico models. Recommendations are made for the development and use of each of the different types of tool, with a particular emphasis on their role in assisting the development of safer products, and to address current and upcoming issues in regulatory toxicology.