All organisms require nitrogen to live and grow. The movement of nitrogen between the atmosphere, biosphere, and geosphere in different forms is described by the nitrogen cycle. This book is an activity of the COST 856 Action on Denitrification. It covers all aspects of the N-cycle: chemistry, biology (enzymology, molecular biology), physics, applied aspects (greenhouse effect, N-pollution problems, practices in farming, in waste-water treatment, and more). In this book, leading editors offer the latest research available on dentrification (reduction of nitrates or nitrites commonly by bacteria- as in soil). It provides details on denitrification and its general role in the environment. It offers latest research in N-Cycle and its reactions. It discusses impacts on various environments: agriculture, wetlands, plants, waste-water treatment and more. It is the only book available in the field since the last 20 years and it contains 27 chapters written by internationally highly recognized experts in the field. It covers all modern aspects, emphasizes molecular biology and ecology. It is written in an easily understandable way.