This book examines the role of modal expressions in various medical genres, as well as pointing out other markers of speaker attitude. Based on new computer-readable data, and combining quantitative and qualitative methods, the book argues that the use of modal expressions reflects the institutional context of medical discourse. Modal expressions are analysed with reference to hedging, reliability, and argumentation, and it is shown that their use in different genres reflects a model of medicine leading from bio-medical hypotheses through assessment to clinical applications. The book also analyses new genres of medical writing that have developed as a response to the increasing amount of medical information. Advertisements are analysed as an example of medicalization, showing how evaluation in the texts is based on medical values.