A consultant is a professional that provides expert advice in a particular domain or area of expertise such as accountancy, information technology, the law, human resources, marketing, medicine, finance or more esoteric areas of knowledge, for example engineering and scientific specialties such as materials science, instrumentation, avionics, and stress analysis. See related Certified Management Consultant and MBA.

How a consultant works

Often the consultant provides expertise to customers which only rarely or occasionally require this particular type of knowledge, thus providing an economy to the client.

More recently the term is also used somewhat euphemistically to mean a person that is only temporarily employed by a company and working under the company's direction in a skill area that the company already has, in other words as an adjunct to the company's core set of employees. This usually implies that the consultant is more expendable when the demand for that particular skill diminishes.

Often a consultant is not an independent agent but is a partner or an employee of a consultancy, that is a company that provides consultants to clients on a larger scale or in multiple, though usually related, skill areas.

A consultant giving career advice and training to an individual or a team is a Coach (see Coaching)

Consultants are very pervasive in upper management in most industries. New trends are spread through corporations by the efforts of consultants, such as Six Sigma.

There are also independent consultants/directors who are interim executives or non-executives with decision-making power under corporate policies/statute. They sit on boards or committees.