Although there is a general scientific consensus that endosymbionts represent a new frontier for drug discovery, this book is the first to explore that possibility. It also takes the novel approach of expanding the concept of defensive mutualisms to evaluate defense against environmental abiotic and biotic stresses. In addressing the topic of defensive mutualisms in microbial symbiosis across this wide spectrum, it includes chapters on defensive mutualistic associations involving multiple kingdoms of organisms in terrestrial and aquatic ecosystems - plant, animal, fungi, bacteria, and protozoans. Authors for the various chapters represent the world authorities in each field.