The aim of preparation of current book is to provide the state-of-the-art knowledge about anaerobes and anaerobic process to undergraduate, graduate and PhD students. During the preparation of book we tried to incorporate contents from very basic like cultivation, handling, preservation and various important process related to anaerobes like biomethanation, anaerobic methanotrophy, solid waste management, anaerobic biohydrogen and biobutanol production, anaerobic nitrogen treatment, anaerobic solid waste management. In addition considering the importance of anaerobes in human health and disease we tried to dedicate a complete section like anaerobic probiotic, anaerobes and human gut microbiology and anaerobes and human infection. Finally we tried to incorporate a chapter on role of anaerobes in animal rumen and food digestion. We believe that current book will serve its aim to satisfy the hunger of knowledge about anaerobes and anaerobic process for the UG, PG and PhD students of Microbiology, Biotechnology, Environmental Science and Biochemistry background.