The horizon is a type of boundary phenomenon. This book embraces the horizon literally understood, as the apparent boundary between earth and sky. It also draws on various metaphorical horizons, tracing the limits of human perception, knowledge and experience. It is especially attentive to the horizons of the Anthropocene, reflecting on their significance for us as a species and as cultural and historical beings, bound to human and other-than-human communities of various sorts. The Adagio poems explore changes that are pending, as well as already underway, in the wake of global warming and sea level rise. Tracing the arc of human perception, they pause in places that are — like our shadow or skin — part us and part of the world that surrounds us.