Pharmacogenetics, the use of genetic testing to prescribe and develop drugs, has been hailed as a revolutionary development for the pharmaceutical industry and modern medicine. Supporters of 'personalised medicine' claim the result will be safer, cheaper, more effective drugs, and their arguments are beginning to influence policy debates. Based on interviews with clinicians, researchers, regulators and company representatives, this book explores the impact of pharmacogenetics on clinical practice, following two cases of personalised medicine as they make their way from the laboratory to the clinic. It highlights the significant differences between the views of supporters of pharmacogenetics in industry and those who use the technology at the clinical 'coal face'. Theoretically, this work builds on the developing area of the sociology of socio-technical expectations, highlighting the way in which promoters of new technologies build expectations around it, through citation and the creation of technological visions.