Speaking in tongues, also known as glossolalia, has long been a subject of curiosity as well as vigorous theological debate. A worldwide phenomenon that spans multiple Christian traditions, glossolalia is both celebrated as a supernatural gift and condemned as semiotic alchemy. For some it is mystical speech that exceeds what words can do, and for others it is mere gibberish, empty of meaning. At the heart of these differences is glossolalia’s puzzling relationship to language. Glossolalia and the Problem of Language investigates speaking in tongues in South Korea, where it is practiced widely across denominations and congregations. Nicholas Harkness shows how the popularity of glossolalia in Korea lies at the intersection of numerous, often competing social forces, interwoven religious legacies, and spiritual desires that have been amplified by Christianity’s massive institutionalization. As evangelicalism continues to spread worldwide, Glossolalia and the Problem of Language analyzes one of its most enigmatic practices while marking a major advancement in our understanding of the power of language and its limits.