Physicians' dual roles - as healer and professional - are linked by codes of ethics governing behaviour and are empowered by science. Being part of a profession entails a societal contract. The profession is granted a monopoly over the use of a body of knowledge and the privilege of self-regulation and, in return, guarantees society professional competence, integrity and the provision of altruistic service. Societal attitudes to professionalism have changed from supportive to increasingly critical - with physicians being criticised for pursuing their own financial interests, and failing to self-regulate in a way that guarantees competence. Professional values are also threatened by many other factors. The most important are the changes in healthcare delivery in the developed world, with control shifting from the profession to the State and/or the corporate sector. For the ideal of professionalism to survive, physicians must understand it and its role in the social contract. They must meet the obligations necessary to sustain professionalism and ensure that healthcare systems support, rather than subvert, behaviour that is compatible with professionalism's values.