In eighteenth-century theater, Diderot’s idea of the "fourth wall" indicated the imaginary partition between the stage and the auditorium. This volume applies Diderot’s conception to today’s proliferating mechanisms of illusion as examined in works by Harun Farocki, Omer Fast, Andrea Geyer, Aernout Mik, Wendelien van Oldenborgh, Judy Radul, Allan Sekula and Ian Wallace among others.