The authors propose a general definition of quality in residency train ing and describe a process for developing the definition. The definition and process go beyond the usual concerns with educational structures and processes and are customer-centered, outcomes-oriented, and consistent with views of quality widely applied in health care, manufacturing, and other businesses. The process begins by listing some of the more important customers of a training program--trainees, patients, funding agencies, health care employers, medical schools and teaching hospitals, and professional organizations--and then considers the needs of those customers. The result is a definition of quality in residency training that is multidimensional and includes aspects of residency training related to the clinical proficiency of trainees, socioeconomic dimensions of training, and ethical concerns. While some measures exist to put this multidimensional definition of quality into operation, much work will be needed to make it useful for the training of residents.