In the context of art, intervention means the uncontrolled and often short period insertion of an individual or group into an art piece or physical location where art is conducted. The intervention strategy changes the premise of the work within context and stimulates the viewer to rethink what the piece is trying to explain. The idea became well known within the century of the 1900's due especially to the development of performance and conceptual art. Famous practitioners of art interventions are Yoko Ono who, through her interactive and extreme pieces of art, broke the barriers of defined art, and Banksy who is known for his public social commentaries put up in graffiti form which have very shocking yet appealing undertones. Interventions can be executed in the form of public installations and performances, or more discreetly by adding, removing, or altering elements in already existing pieces. Most of these set out to create discourse, breach the status quo, or create awareness of the unnoticed issues in the field of art. In effect, social commentaries become the means of changing the most basic assumptions about art and its spectators. Interventions remain the most powerful forms of art in which a direct audience is intended by the creator.