Here is an excerpt from my book — Keith Johnstone: A Critical Biography — that briefly defines the Impro System:
The Impro System (i.e., my term for denoting Keith’s theories, pedagogy, techniques, exercises, games, and terminology) is Keith’s most important contribution to theatre practice worldwide. The Impro System is an approach to actor training and theatre practice that encourages spontaneous, collaborative creation using the intuitive, uncensored imaginative responses of the participants. Since 2005, I have been referring to Keith’s process as a “system” because, like other complex systems — the solar system, transportation systems, the nervous system — optimal functionality depends on all components working harmoniously. General System Theory is a scientific discipline postulated by Austrian biologist Ludwig von Bertalanffy in the 1950s. In very basic terms, Bertalanffy’s theory dictates that all parts of the system interact with each other directly or indirectly but privileges the wholeness of the system over its parts. In this sense, the Impro System is a system because it cannot be reduced down to its parts without decreasing its efficacy. When students apply the theatre games without understanding the theory or when teachers teach the exercises without understanding Keith’s pedagogy, the process is compromised.
The “Circle of Probability” is another concept of Keith’s that underpins the entire Impro System. My essay “Keith Johnstone’s ‘Circle of Probability’: A Concept for Creating Stories That Engage Audiences” was published in Theatre Topics March 2013 issue. CLICK HERE to read an excerpt from the essay and/or to purchase a copy.