The control of unintended variation is an objective central to modern industrial quality management methods, based largely on the theoretical work of Walter A. Shewhart. As industrial quality management techniques find their place in health care, professionals may feel threatened by the effort to reduce variation. Understanding may reduce this fear. Variation of the types addressed in quality control efforts erodes quality and reliability, and adds unnecessarily to costs. Such undesirable variation derives, for example, from misinterpretation of random noise in clinical data, from unreliability in the performance of clinical and support systems intended to support care, from habitual differences in practice style that are not grounded in knowledge or reason, and from the failure to integrate care across the boundaries of components of the health care system. Quality management efforts can successfully reduce each of these forms of variation without insult to the professional autonomy, dignity, or purpose of health care professionals. Professionals need to embrace the scientific control of variation in the service of their patients and themselves.