This chapter will explore professionalism historically, from the work of Gregory and Percival in the eighteenth century, though to contemporary “new professionalism.” The chapter will identify how the core traditional values of professionalism, in particular commitments to an other-regarding social ethic and to maintaining high levels of scientifically informed expertise, alongside the defense of professional self-regulation, have been articulated and challenged. Classic accounts of professionalism are found in the work of Durkheim, Tawney, and Parsons. Critics have argued that professionalism is self-serving, particularly insofar as a professional ethic has justified the autonomous self-regulation of the profession. Over the last 30 years, responses to the perceived crisis of professionalism—due to the loss of broad public trust in the professions, changes in the nature of professional expertise, and increased demands for external regulation—have precipitated a series of more or less radical responses. New professionalism began to question the desirability of professional autonomy and self-regulation and to articulate a professionalism committed to public engagement and the acceptance of external regulation. It may nonetheless be argued that any concept of professionalism faces continuing challenges as the professions adapt to ongoing technological, political, and cultural change.