This thesis discusses the use of clowns and clowning in avant-garde theatre. It concentrates on two avant-garde works that experiment with traditional forms of clowning: Antonin Artaud's The Philosopher's Stone (1930-31), and Samuel Beckett's Krapp's Last Tape (1958). The thesis examines the forms of clowning that are employed in the dramatic works. In The Philospher's Stone, Artaud draws on the plot and characters Commedia dell'Arte, and in Krapp' s Last Tape, Beckett uses recognisable traits from modern forms of clowning such as the circus and silent film. Clowning and avant-garde theatre are generally thought to be antithetical. Whereas the avant-garde is defined by its rejection of the artistic practices of past and its search for the new, the clown tradition is rooted in the repetition of old conventions and techniques. This thesis argues that Artaud and Beckett use clowning in ways that reflect their individual artistic concerns. Artaud creates a non-verbal pantomime that is rooted in physical images and the basic, life-producing processes of the body. Beckett uses clown gags to illustrate the conflict between mind and body, and to parody the values of serious literary art. The avant-gardists expose and exploit complications within clowning: Artaud accentuates the sexual and violent undertones of clown humour, and Beckett emphasises the presence of misery and unhappiness within clowning.