Expressionism was a theatrical movement which developed in Europe in the first decades of the 20th Century.
Rebellion
The Expressionism movement was a rebellion against Realism (or Naturalism), aiming to explore:
The psychology of its central characters.
The effects of social and political systems on its characters.
Methods
In reacting against Realism, Expressionist theatre used new and innovative methods:
Abstract, often ‘empty’ stage designs.
Intense lighting (often from unusual angles, creating stark contrasts between light and shadow).
Experimental music.
Expressionist cinema
The style of Expressionist theatre of this period can probably best be appreciated by watching examples of Expressionist cinema of the period such as Nosferatu (1922) and Metropolis (1927).