The book will broadly examine and synthesize aspects of the evolution, development, structure and function of the avian respiratory system and the lung-air sac system. The following questions will be answered: from where did the avian respiratory system originate?; how did it form?; how is it built?; how does it function? and; how does the functional design of the system allow and sustain powered flight and flight at high altitude? The chapters will be contributed by an international group of researchers who are renowned authorities in their areas of specialization.