We explore heterogeneity in the use of an organization-wide information technology (IT) by both individuals and groups in a professional organization. We study electronic medical record use by physicians and clinic work groups in two medical practices operating within one multi-specialty health care clinic. Data collection methods include interviews, non-participant observations, and questionnaires. Drawing on theories of professional organizations and complex adaptive systems, we offer as an explanation of heterogeneity in IT use by individuals that IT use is a function of professional values and expertise and of heterogeneity of IT use in groups the insight that IT use at a collective level is an emergent property arising from the interactions of diverse, learning agents. This study contributes to information systems research by enriching current understandings of IT use and by providing new insights about heterogeneous IT use in professional organizations.