An account of the different morphologies of vertebrate respiratory organs and structures. It explains the essence of different functional designs and strategies that have adaptively developed for the acquisition of molecular oxygen and elimination of carbon dioxide. The origins of the various respiratory systems are presented and debated from evolutionary, phylogenetic, behavioural and ecological perspectives. The book carefully outlines the interactions between the environment (the physical realm) and evolution and adaptation (the biological domain) that have set the composition and patterning of extant animal life.