Evidence-based medicine (EBM) aims to address the persistent problem of clinical practice variation with the help of various tools, including standardized practice guidelines. Based on a systematic evaluation of the available scientific evidence, these guidelines offer recommendations for clinicians about details of patient care and clinical decision making. Because clinical practice guidelines specify how health care should be performed, they could be considered a threat to clinical and professional autonomy. Inspired by the theory of countervailing powers, this article explores how clinical practice guidelines have shifted the focus of professional power from autonomy to accountability. Professional organizations develop clinical practice guidelines as a service to their members but do not require strict adherence to the guidelines. Indeed, implementation studies show at best a modest change in clinical behavior. Such non-adherence might render a profession vulnerable, however, when third parties seize upon guidelines and offer financial incentives to keep clinicians accountable for delivering optimal patient care.