The view of nature as `red in tooth and claw', as a jungle in which competition and predation are the predominant themes, has long been important in both the scientific and popular literature. However, in the past decade another view has become widespread among ecologists: the idea that mutualisms--mutually beneficial interactions between species--are just as important as competition and predation. This book is one of the first to explore this theme. Ideas and theories applicable to all sorts of mutualisms are presented and, where appropriate, examined in the light of concrete data. Themes explored include: the organisms involved, both animal and plant; how specializations evolved once mutualisms formed; how mutualisms affect population dynamics and community structure; and the role of mutualisms in different environments. The book will be of special interest to ecologists and a wide range of biologists.