We have entered a new era of medicine in which both the interest of scientific rigor and pressure from health care purchasers demand increased adoption of empirically based standards of care. Certain therapeutic areas have seen rapid transformation from a model in which care is based on a clinician’s intuition to one based on therapies and standards backed by substantial clinical evidence. The condition of non–ST-elevation acute coronary syndromes, a leading cause of death in industrialized nations, provides an excellent example of this transformation and a potential model for other areas of disease treatment. This article discusses the cycle of quality (the conceptual basis for quality improvement in non–ST-elevation acute coronary syndromes), the approach taken by the American College of Cardiology and the American Heart Association in developing their clinical practice guidelines, the use of performance indicators in clinical practice, and the ever-increasing evidence that adherence to practice guidelines and attention to performance measures result in improved patient outcomes.