The Archaea, or archaebacteria, constitute the fifth kingdom of living organisms, as distinct from true bacteria as from fungi, animals, and plants. They were very likely the first life forms, from which all other living things evolved, because they are naturally adapted to thrive in the anoxic extreme environments that prevailed when life originated on the earth. This book traces their history in nature and covers their discovery, evolution and biology. '... most biologists concerned with life's beginnings, the phylogeny of modern taxa and the adaptability of cellular machineries will appreciate this volume.' P.G.Willmer, Nature