The desire to imitate others or to adopt an imaginary persona is natural, as is the pleasure of watching others perform. When the impulse to imitate and observe is formalized, the actor and theater are born. An actor needs to develop great physical and vocal flexibility and control in order to create believable, compelling characters. From the nineteenth century to the present, many plays have been written in a realistic, lifelike style. In order to perform these plays, the Russian director Constantin Stanislavski developed a system for realistic acting that has become widely used throughout the world. Other exercises and tasks have been developed to train performers, including circus techniques and tai chi. Avant-garde theatre often makes additional demands on the performer that are very different from those of a realistic play.

Audiences should familiarize themselves with the problems and techniques of acting in order to judge performances properly.