This chapter examines The Sirens of Titan (1959) through the prism of new materialist theory. Sirens, Vonnegut’s only unambiguously ‘science fiction’ novel, is a novel of objects in space. It is the solar system itself that provides Vonnegut with his subject and setting; it is a novel that particularly reflects Vonnegut’s interest in contemporary science and the questions that inform it. This chapter begins by exploring the peculiar nature of materiality with reference to Graham Harman’s object-oriented ontology. Contra to relational ontologies, Harman asserts the absolute primacy of objects, expanding Husserlian phenomenology and Heidegger’s tool-being to the non-human realm and claiming that all objects are irreducible to their features. Yet, with reference to Karen Barad’s quantum-influenced theory of intra-activity – in which relations or situations in some sense precede the existence of matter – another way of understanding reality is also explored in Sirens. From this perspective, there are no detached observers, agency is spread across apparatuses, and systems are endlessly imbricated within one another. A newly affirmative posthumanist ethic emerges at the end of the novel: situational and communal rather than bounded and individualist, agentive rather than autonomous, and materialist/monist rather than transcendentalist/dualist.