In this classic work that continues to inspire its many readers, Jim Lovelock puts forward his idea that the life of earth functions as a single organism. Written for non-scientists, Gaia is a journey through time and space in search of evidence with which to support a new and radically different model of our planet. In contrast to the conventional belief that living matter is passive in the face of threats to its existence, the book explores the hypothesis that the Earth's living matter - air, ocean, and land surfaces, forms a complex system which has the capacity to keep Earth a fit place for life. Since Gaia was first published, many of Jim Lovelock's predictions have come true and his theory has become a hotly argued topic in scientific circles. In a new Preface to this revised impression, he outlines the present state of the debate.