A consultant is usually an expert or a professional in a specific field and has a wide knowledge of the subject matter. The role of consultant outside the medical sphere (where the term is used specifically for a grade of doctor) can fall under one of two general categories:
 Internal consultant – someone who operates within an organization but is available to be consulted on areas of specialism by other departments or individuals (acting as clients); or
 External consultant – someone who is employed externally (either by a firm or some other agency) whose expertise is provided on a temporary basis, usually for a fee. As such this type of consultant generally engages with multiple and changing clients.