Teaching medical professionalism is a fundamental component of medical education. The objective is to ensure that students understand the nature of professionalism and its obligations and internalize the value system of the medical profession. The recent emergence of interest in the medical literature on professional identity formation gives reason to reexamine this objective. The unstated aim of teaching professionalism has been to ensure the development of practitioners who possess a professional identity. The teaching of medical professionalism therefore represents a means to an end.The principles of identity formation that have been articulated in educational psychology and other fields have recently been used to examine the process through which physicians acquire their professional identities. Socialization-with its complex networks of social interaction, role models and mentors, experiential learning, and explicit and tacit knowledge acquisition-influences each learner, causing them to gradually "think, act, and feel like a physician."The authors propose that a principal goal of medical education be the development of a professional identity and that educational strategies be developed to support this new objective. The explicit teaching of professionalism and emphasis on professional behaviors will remain important. However, expanding knowledge of identity formation in medicine and of socialization in the medical environment should lend greater logic and clarity to the educational activities devoted to ensuring that the medical practitioners of the future will possess and demonstrate the qualities of the "good physician."