There is a blue hole in environmental history. The thirteen essays in this very accessible collection fill it by closing the gap between land and sea, by exploring the ways the earthly and maritime realms influence one another. What has too often been described as the ‘eternal sea’ is shown to be remarkably dynamic. Ranging widely from Australia to the Arctic, from ocean depths to high islands, a new generation of humanists and scientists trespass the boundaries of their own fields of inquiry to tie together human and natural histories. They reflect contemporary concerns with declining fisheries, damaged estuaries, and vanishing coastal communities. Here the history of oceanic sciences meets that of literary and artistic imagination, offering vivid insights into the meanings as well as the materiality of waves and swamps, coasts and coral reefs. In their introduction, John Gillis and Franziska Torma suggest the directions in which the fluid frontiers of marine environmental history are moving.