Being undercover is disguising one's own identity or using an assumed identity for the purposes of gaining the trust of an individual or organization to learn secret information or to gain the trust of targeted individuals in order to gain information or evidence. Traditionally it is a technique employed by law enforcement agencies around the world and a person who works in such a role is commonly referred to as an undercover agent.

Undercover work has been used in a variety of ways throughout the course of history, but the first organized undercover program was first employed in France by Eugène François Vidocq in the early 19th century. The English set up the Special Irish Branch (later to be named just Special Branch) in 1883 and in the United States the ‘Italian’ Squad was set up in 1906 before different federal agencies started to run their own undercover programs.

There are two principal problems that can affect agents working in undercover roles. The first is the maintenance of identity and the second area is the reintegration back into normal duty.