Taking the French oncology sector as a case study, this paper shows that guidelines are used strategically by individual physicians and groups of physicians. While some studies have made convincing arguments about the rise of guidelines as a manifestation of a new type of objectivity, this case study provides evidence that the proliferation of medical guidelines is also the result of an attempt by some physicians to improve their positions relative to competing groups. Guidelines could indeed be strategic resources used by professional actors at the expense of other professionals in order to (1) maintain a sufficient amount of activity and (2) increase control over therapeutic decisions. The study also points to other kinds of changes that guidelines may influence, beyond medical practices and coordination: namely, the evolution of the structure of power relationships inside the medical profession. A perspective on the sociology of organizations, which places concrete exchange and bargaining relations at the core of its analysis and treats social control as being continually challenged and (re)produced, helps to identify other reasons for why standardization does not prevent local specificities and may even enhance them.