A wide-ranging account of the twenty-first century's fascination with the weird. Twenty-first-century fiction and theory have taken a decidedly weird turn. They both show a marked interest in the nonhuman and in the preternatural moods that the nonhuman often evokes. Writers of fiction and criticism are avidly experimenting with strange, even alien perspectives and protagonists. Kate Marshall's Novels by Aliens explores this development broadly while focusing on problems of genre fiction. She identifies three key generic hybrids that harness a longing for the nonhuman: the old weird, an alternative tradition within naturalism and modernism for the twenty-first century's cowboys and aliens; cosmic realism, the reach for words legible only from space in otherwise terrestrial narratives; and pseudoscience fiction, which imagines speculative futures beyond human life on earth. Offering sharp and surprising insights about a breathtaking range of authors, from Edgar Rice Burroughs to Kazuo Ishiguro, Willa Cather to Maggie Nelson, Novels by Aliens tells the story of how genre became mood in the twenty-first century.