Healthcare information systems (IS) such as Computerized Physician Order Entry (CPOE) systems have the potential to improve efficiency of healthcare, lower costs, and reduce medication errors. However, previous studies have also described various issues arising from the use of these systems. A key issue pertains to physician resistance to CPOE, causing low usage or the abandonment of system implementations. Despite considerable research on CPOE, there is still a lack of understanding about the acceptance and use of these systems by physicians. This paper aims to address this gap by applying the theoretical perspective of professionalism, a type of institutional logic to understand this phenomenon. We thereby develop a model to explain the impact of physicians’ professional practice arrangements and seniority on their usage of CPOE. The model will be tested using the survey method by collecting data from physicians on their use of CPOE. Objective measures to determine system usage will be utilized if available. In this manner, this study intends to contribute to research and practice on the use of healthcare IS.