Exploring how modernism registered shock experiences of the microscopic and extended vision in prose fiction through the work of four modernist writers - D. H. Lawrence, Marcel Proust, Virginia Woolf, and Samuel Beckett - this book is the first substantial study of the interrelations between microscopy and modernist fiction. Illustrating ways in which optical instruments had the capacity to change, displace and reframe ideas of what the world is like, this book argues that encounters with the microscopic are often depicted as thresholds between the human and the non-human, in ways that reverberate through modernist fiction. Exploring a period of significant developments in microscopical tools and techniques, from the light microscope to the electron microscope, this book traces a shift that reconfigured the limits of the observable.