This book describes the ecology of sea ice algae and other microorganism such as bacteria, meiofauna, and viruses residing inside or at the bottom of the sea ice, called the sympagic biota. Organisms such as seals, fish, birds, and polar bears rely on sea ice but are not part of this biota. A distinct feature of this ecosystem is the disappearance (melt) every summer, and the ice's re-establishment in autumn and winter. Arctic Sea Ice Ecology is organized by season, describing the physical, optical, biological, and geochemical conditions typical of each. These are exemplified by case studies based on the authors' fieldwork in Greenland, the Arctic Ocean, and Antarctica, but with a focus on Arctic conditions. The sea ice ecosystem is described in the context of climate change and effects of a decreasing summer ice extent in the Arctic Ocean. Arctic Sea Ice Ecology contains an up-to-date description of the most relevant methods and techniques applied in sea ice ecology research.