The introduction makes the case that while theatre has tended to be ignored or marginalised in modernist studies, it deserves a central place in accounts of modernism alongside poetry, prose, cinema, and the visual arts. It further contends that while there is an impressive variety amongst its practitioners, the hallmarks of modernist theatre are antagonism and provocation. Indeed, modernist theatre-makers rebelled against dominant genres, conventions, institutions, and audiences by creating new artistic forms and advocating for different values and worldviews. In so doing, this chapter argues that scholars need to go beyond the usual Euro-American cultures to consider how modernist theatre was manifested in the wider world and to recalibrate the historical trajectory of modernism that such broader geographies demand.