At stake are issues fundamental to bio-science, medical treatment and patients’ health in wider society, such as what kind of knowledge is judged necessary to decide whether or not a drug is a carcinogen and when does a drug pose a significant carcinogenic risk to humans? Given that all new drugs, many with prospective world-wide markets, are potential carcinogens, this is an extremely important socio-political issue, but has been largely neglected in social science and indeed medicine. This is the first social science/policy book on the geneticization of international pharmaceutical testing and pharmaceutical toxicology. The book challenges the idea that the geneticization of carcinogenic risk assessment is simply a reflection of inevitable progress in laboratory science. Rather, a basic contention of this book is that such developments are framed and constituted by discursive and non-discursive practices, involving confluence of technical manipulations and socio-political accomplishments. The in-depth empirical research forms the basis for explaining the social shaping of carcinogenic risk assessment, the social meaning of its geneticization and the public health implications of the consequent ‘reduction’ in this regulatory science for society.