The sociology of work sees a number of occupations evolving over time and becoming professions. All professions are thus occupations but not all occupations are professions. A profession is an occupational group that is largely self-regulating.
Such a 'professional' group has the legitimate authority to set its own standards for entrance, to admit new members, to establish a code of conduct, to discipline members and it claims to have a body of knowledge which legitimizes its autonomy.
Examples of professions and professionals include Doctors, Lawyers, Clergy, Surveyors, Social Workers, Nurses, Pharmacists, Accountants, Veterinarians, Pilots, Engineers, Teachers, Diplomats, Commissioned Officers, Professors, Librarians, Archivists, Architects, Physical Therapists, Dentists and Physicians. The first three, that is, Doctors, Lawyers and Clergy were the only professionals with a unique profession.
Other groups, such as police officers can be seen as having some of these attributes and can be described as professionalizing - in the process of becoming a profession. The process by which a profession arises from a trade or occupation is often termed professionalization and has been described as one, "starting with the establishment of the activity as a full-time occupation, progressing through the establishment of training schools and university links, the formation of a professional organization, and the struggle to gain legal support for exclusion, and culminating with the formation of a formal code of ethics." - Jennifer Roberts & Michael Dietrich, Conceptualizing Professionalism: Why Economics Needs Sociology, The American Journal of Economics and Sociology, Oct, 1999.
Professions are generally regulated by statute, with professional bodies regulating their professional conduct and whose function is to define, promote, oversee, support and regulate the affairs of its members. These bodies are responsible for the licensure of professionals, and may additionally set examinations of professional competence and enforce adherence to an ethical code of practice.