Laying the intellectual groundwork for the book, this chapter gives an in-depth introduction to new materialist philosophy and its relationship to other 20th and 21st century theoretical movements and discussions, as well as to key concepts used in the study: affect, old and new materialism, dramatic and postdramatic theatre, biopolitics, sovereignty and economics, fascist immunitarianism, and others. This Introduction also announces the book’s focus on modern theatre: The plays explored map the universality of the “flesh” in (politically democratic, post-Darwinian) modernity, an ontological anxiety located at the threshold between materiality and human sovereignty, in other words the danger -- or, depending on the writer, the promise -- posed in post-transcendental modernity by the inability of keeping human subjectivity separate from nonhuman vitality. Rather than considering them in isolation, the book explores the entanglement of human culture with diverse forms of agentive materiality – economic, embodied, and inorganic.