Wynia and colleagues propose a definition of professionalism as a belief system by which to shape health care rather than a list of values and behaviors. The belief that professionalism is the best way to organize and deliver health care constitutes a promise to society. The notion that the medical profession as a whole as well as its individual members should be held accountable to standards of competence, ethical values, and interpersonal attributes developed, declared, and enforced by the profession itself is also a promise to society. The author argues that good promises offer a stabilizing influence over the inherent uncertainty in human relationships and may provide the ground for a lasting trustworthy relationship between the medical profession and society; however, the professionalism belief system itself is vulnerable if the promise is breached. The modern world has challenged the professionalism model of organizing health care, and individual practitioners as well as their professional organizations are seeking clarity about what professionalism means given current realities. This commentary reflects on these circumstances and provides some recommendations for developing a construct of professionalism.