On rocky coastlines, receding tides leave standing pools that have long held a fascination for the amateur seashore naturalist, revealing glimpses of colourful and curious marine plants and animals. Animal diversity is far greater in the sea than in terrestrial or freshwater habitats, and the hugely varied fauna of rock pools reflects that fact. Rock pools also undergo dramatic shifts in temperature, salinity and pH, making such habitats crucibles of adaptation and change. This Naturalists' Handbook offers a comprehensive introduction to this mysterious world, with chapters covering rock-pool ecology, seaweeds, animals, identification and guidelines for possible fieldwork and further study. Also presented are detailed keys to all the main groups likely to be encountered when rockpooling around Britain and Ireland – from sea squirts to chitons, from anemones to sea spiders, from amphipods to fishes. Rock pools is an indispensable tool in discovering these kaleidoscopic habitats and their multitudinous inhabitants.