There is now an increased awareness of the importance of polar regions in the Earth system, as well as their vulnerability to anthropogenic derived change, including of course global climate change. This text is the latest edition of this book and offers an introduction to polar ecology. It has been revised and updated, providing expanded coverage of marine ecosystems and the impact of humans. It incorporates a comparison of the Arctic and Antarctic systems, with a particular emphasis on the effects of climate change, and describes marine, freshwater, glacial, and terrestrial habitats. Much emphasis is placed on the organisms that dominate these extreme environments although pollution, conservation, and experimental aspects are also considered.