The post-avant-garde is one of the most relevant phenomena of the Italian theater in the 1970s and early 1980s. Its main characteristic is to deconstruct theatrical language into its “phonemic” elements, reducing it to its pure signifiers. This chapter reconstructs the scenic and theoretical features of the post-avant-garde, particularly through the analysis of one of its main protagonists: Federico Tiezzi. This examination of the post-avant-garde is undertaken not only to offer useful information for the history of international New Theater but also to investigate the relationship between theater and performance art. The meeting ground between the two terms is what we can call “performative theater”—that is, theater that is not based on a narrative background or literary material but on physical action carried out in an actual space and time. The chapter shows how the post-avant-garde’s analytical approach to theatrical language, breaking the relationship between the signifier and the signified, represents a foundational moment in this model of theater, and thus provides a key to understanding the development of a new theatrical genre in the second half of the twentieth century.