Different modes of practice organization may result in advantages for physicians and their patients. Compared with solo practice, group practice may produce economies of scale, efficiencies in health care delivery, and improvements in the quality of care. However, in Canada assessment of the implications of differences in practice organization have been impeded by a lack of relevant data and a tendency to treat practice type as a dichotomous variable. Conventional solo/group distinctions fail to address the significance of the growing number of medical practices that are neither solo nor group, but combinations of both, and they obscure the policy implications of the growing number of physicians in institutional as opposed to private practice. This paper develops and applies a theoretically based typology of practice organization to data collected as part of a national survey of 2,398 Canadian physicians conducted in late 1986 and early 1987. The analysis identifies six practice types, describes their distribution and operating characteristics, and identifies the characteristics of physicians working in them.