This book has been cunningly designed to provide an overview of our current knowledge about the innate immune systems of these three types of organisms. It not only covers the innate immune mechanisms and responses of such diverse organisms as plants, Cnidaria, Drosophila, urochordates and zebrafish, but also the major receptor systems in mammalians and humans. It delves too into the central defense mechanisms, antimicrobial peptides and the complement system.