There has been increasing emphasis on professionalism in medical education over the past several decades, initially focusing on bioethical principles, communication skills, and behaviors of medical students and practitioners. Authors have begun to discuss professional identity formation (PIF), distinguishing it as the foundational process one experiences during the transformation from lay person to physician. This integrative developmental process involves the establishment of core values, moral principles, and self-awareness. The literature has approached PIF from various paradigms-professionalism, psychological ego development, social interactions, and various learning theories. Similarities have been identified between the formation process of clergy and that of physicians. PIF reflects a very complex process, or series of processes, best understood by applying aspects of overlapping domains: professionalism, psychosocial identity development, and formation. In this study, the authors review essential elements of these three domains, identify features relevant to medical PIF, and describe strategies reported in the medical education literature that may influence PIF.