This short book attempts to give a reader who has a basic biochemical and microbiological background (one to two years at University level) an idea of the ecological, biochemical, physiological and biotechnological importance of methane, methanol and related compounds in the microbial world. Because the book covers several different scientific disciplines, readers may encounter unfamiliar terminology. The glossary at the end of the book defines the more obscure of these. The book has been written during a period of heavy teaching commit­ ments, and despite the helpful comments of many colleagues, it is likely that errors have crept in. As I have no co-author whom I can blame, I must accept sole responsibility for these! I wish to thank the many friends, students and colleagues who have read all or part of the manuscript: Charlie Bamforth, Rick Gibson, Jeff Green, Theo Hansen, Wim Harder, Geoff Haywood and, above all, Hans van Dijken.