Religion made the theatre modern. Since the late nineteenth century, theatre theorists have asserted that drama's origins lie in religious ritual. In this ambitious study, Rebecca Kastleman traces the surprising effects of that claim for the modern and contemporary stage. Across lucidly written chapters, she tracks the 'modern drama of religion,' a movement rooted in both the many modern plays that engage directly with religion and the dramatic debut of new religious practices in the modern theatre. Such works serve as crucibles for catalyzing skepticism, dissolving some religious attachments and strengthening others. Modern playwrights' fascination with religion expanded the frontiers of theatrical experimentation, such that in modernity, the purported origin of theatre in religious ritual came to signify the cutting edge of artistic invention. Spanning drama, performance, modernism, and religious studies, this study powerfully reconfigures the relations between all these fields.