In the 1960s 'groupishness' appears to have been a common phenomenon, especially amongst the young. In America, a major movement developed that combined the politics of the New Left with what are often described as 'countercultural' influences - sexual freedom, drug experimentation, Eastern mysticism, and communal living - to comprise 'the Movement'. Group experimentation was a cornerstone of the Movement. American radical theatres were a cornerstone of the Movement. These theatres experimented extensively with group work, usually under the rubric of 'collective creation'. This thesis examines three American radical theatres of the 1960s, the Living Theatre, the San Francisco Mime Troupe, and the Performance Group, in the context of their ideas and ideals about the group as they were expressed both on stage and off. Using concepts advanced by W.R. Bion, Erving Goffman, Rosabeth Kanter and Victor Turner, it is argued that an underlying 'ultrademocratic', i.e., anti-hierarchical-yet-individualistic, 'liminoid' group paradigm affected all three radical theatres to varying degrees. This paradigm combined an idea of the group as a potential threat to individual autonomy with an idealised image of the group as a conduit to communitas. The ways in which these theatres sought to create, express and reconcile the existential, normative and ideological dimensions of communitas, and their attendant efforts at celebrating individuality or effacing individualism are considered. The Living Theatre's Paradise Now (1968), the San Francisco Mime Troupe's The Minstrel Show or Civil Rights in a Cracker Barrel (1965), the Performance Group's Dionysus in 69 (1968), and the concept of 'Guerrilla Theatre' as espoused both by the Mime Troupe and a Mime Troupe offshoot, the Diggers, are analysed in this regard, as are other particular productions. Detailed attention is given to the position of the director as leader in a climate of ultrademocracy.