It has been great fun to write this book, even though it has taken longer than planned, and occasionally been exasperating. The most difficult problem was deciding what to exclude among so many interesting things, because the available material usually exceeded the space. Because a book like this covers so many aspects, each component must be limited. This book is intended for graduate and undergraduate students as well as professional scientists who want to work with animal flight or to gain some insight into flight mechanics, aerodynamics, energetics, physiology, morpho­ logy, ecology and evolution. My aim has not been to give the whole mathe­ matical explanation of flight, but to provide an outline and summary of the main theories for the understanding of how aerofoils respond to an airflow. I also hope to give the reader some insight into how flight morphology and the various wing shapes have evolved and are adapted to different ecological niches and habitats.