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In modern usage, professionals tend to have certain qualities in common. A profession is always held by a person, and it is generally that person's way of generating income. A professional is usually licensed and regulated by a particular quasi-governmental organization, such as a bar association. To get a license, the professional must receive certain education (such as graduating from medical school), and pass further examinations and/or apprenticeships. Professionals are also subject to discipline, including revocation of their license, if they breach the standards set out by the governing organization. People without licenses are usually prohibited by law from engaging in those activities practiced by professionals.
There is no standard definition of a modern professional, however. Beyond the classical examples (lawyers, doctors, etc.) there are many groups that claim status as a profession, and many who would dispute that status. The existence of a traceable historical record of notable members of the profession can serve as an indicator of a profession. Often, these historic professionals have become well known to laypersons outside the field, for example, Clarence Darrow (law), Edward Jenner (medicine), and Florence Nightingale (nursing). In modern times, however, there is no standard definition.

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In a more restrictive sense, profession often refers specifically to fields that require extensive study and mastery of specialized knowledge, such as law, medicine, the military, nursing, the clergy or engineering. In this sense, profession is contrasted with occupation, which refers generally to the nature of a person's employment.
Terms such as occupational serve the purpose of upholding the distinction between professionals and others who for their living are dependent on their work rather than on their economic wealth. Such usage avoids the confusion caused by vague usage of the words professional and professionalism to express prestige, approval or a sense of exclusivity.
Sociologists have been known to define professionalism as self-defined power elitism or as organised exclusivity along guild lines, much in the sense that George Bernard Shaw characterised all professions as "conspiracies against the laity". Sociological definitions of professionalism involving checklists of perceived or claimed characteristics (altruism, self-governance, esoteric knowledge, special skills, ethical behaviour, etc) became less fashionable in the late 20th century.
The distinction between laypersons and professionals denotes the critical aspect of more liberal definitions of a profession: being paid for the work. As such, ball players and movie makers may be professionals, although their work does not fit the strict definition offered above