This volume provides a novel insight to the evolutionary and comparative aspects of nitric oxide- nitric oxide synthase system as a central regulator of invertebrate and vertebrate homeostasis. By critically selecting and summarizing the ever–increasing number of original studies, these presentations review a variety of important signalling and modulatory roles played by nitric oxide at molecular, cell, organ and organ system levels. It addresses not only specialists and graduate students in the field, but also all biologists concerned with how this unique, gaseous, pleiotropic molecule has been employed by living systems, uncovering a new dimension of the wonders of life.