A witness is someone who perceives an incident using any of the five senses, though the most common form of witnessing something is of course, sight. The term is generally applied in a legal context, and refers to any individual who may be called upon to testify at a trial, either by a prosecuting attorney or by a defense attorney. There are also people identified as expert witnesses, which are those that may not necessarily be privy to the exacting details of an incident, but may serve in an advisory capacity. During a criminal trial such witnesses may include law enforcement personnel, scientists or members of the medical community.

Examples of witnesses can be found in abudance in any television program of the legal drama subgenre such as The Defenders, The Guardian, L.A. Law, Law & Order and Boston Legal.