Since the 1990s, there has been an increasing presence of performers on the stages of professional theater who do not meet the criteria for professional actors. Under what premises do these performers appear in the theater landscape without a drama school diploma? The spectrum ranges from playing with authenticity to the participation of marginalized groups, as well as the "freaks" in Christoph Schlingensief's work and the performers of Theater Hora, professional actors with intellectual disabilities. The book traces the heterogeneous phenomenon of amateurs in contemporary theater: from everyday experts to citizen stages that institutionalized theater with amateurs. Other forms of theater practice that stand in a dynamic contrast to "expert theater" are also brought into focus: the vibrant amateur theater of Switzerland and theater.