A large number of comprehensive publications has been devoted to the Antarctic, to its plant and animal life. It is therefore relatively easy to familiarize oneself with the current state of Antarctic research. Nothing comparable is available for the Arctic. The heterogeneity and richness of the northern polar regions seem to have discouraged any attempt at a synthethic approach. This book has evolved from an attempt to summarize the results of 15 years of ecological and physiological research work in the Arctic - mostly on Spitsbergen. The necessity of comparing our results and the ecological conditions of Spitsbergen with other arctic regions grew into a full-sized book on arctic animal ecology. It is not meant as an exhaustive survey ofthe relevant literature. Instead I have tried to show how closely the various fields of research are interwoven, how many questions can be solved if only notice is taken of fellow scientists and their results, and how much arctic animals have in common. This book would not have been possible without the helpfulness of many colleagues. Above all I should like to mention Professor Ronning and Professor Solem of Trondheim University (Norway), Professor Arnthor Gardasson of Reykjavik University (Iceland), Dr. NettIeship, Dr. Oliver and Dr. Ryder of Canada and Professor West of Fairbanks University (Alaska, USA).