This chapter outlines a series of case studies for chemical category formation and read­across. The main focus being around the use of mechanistic information related to the molecular initiating event encoded as in silico profilers in tools such as the OECD QSAR Toolbox. The chapter also outlines an example of the use of 2D chemical similarity in the formation of categories using freely available tools such as Toxmatch. All of the examples, including the associated data, use freely available computational tools and data.