How do sandhoppers inherit an inbuilt compass from their parents? What is it that prawns know? How do crabs understand the tides? How can the death of one winkle guarantee the lives of its companions? The physics of the seas, the biology of anemone and limpet, the long history of the earth itself, the governing myths of those who have lived and survived here: the intertidal has been the scene for all kinds of scientific discovery; from the workings of evolution to the intricacies of biological networks. But its story is as much human as natural history: how far should our own lives be understood as an aspect of ecology? Do our buried beliefs about the tidal sea reflect a fundamental understanding of our relationship to nature? Is it the shifting condition of the tidal world, its pervasive uncertainty, its fierce interfolding of opportunity and threat, that makes it one of the most emblematic and revelatory habitats on earth?