This book is appropriate for advanced undergraduate students of micro- biology and biological sciences in universities and colleges, as well as for research workers entering the field and requiring a broad contemporary view of anaerobic bacteria and associated concepts. Obligate anaerobes, together with microaerophils, are characterized by their sensitivity to oxygen. This dictates specialized laboratory methods- a fact which has led to many students being less familiar with anaerobes than their distribution and importance would warrant The metabolic strategies such as methanogenesis, an oxygenic photosynthesis and diverse fermenta- tive pathways which do not have equivalents in aerobic bacteria also make anaerobes worthy of attention. In these limited pages an attempt has been made to cover the varied aspects of anaerobic bacteria, and a bibliography has been included, which will allow individual topics to be pursued in greater detail. We are grateful to Mrs Winifred Webster and Mrs Hilary Holdsworth for typing the manuscript and to the Leeds University Audio Visual Service for preparing the figures. Finally, our thanks go to the students, postgradu- ates and wives who read and criticized the manuscript.