20th Century Drama
Twentieth-century theatre describes a period of great change within the theatrical culture of the 20th century. There was a widespread challenge to long established rules surrounding theatrical representation; resulting in the development of many new forms of theatre, including modernism, Expressionism, Impressionism. political theatre and other forms of Experimental theatre, as well as the continuing development of already established theatrical forms like naturalism and realism.
Answers.com Overview of theatre through history, including 20th century drama.