<P>David E. Alexander's fascination with the many animals and plants that have harnessed the air is evident in <I>Nature's Flyers: Birds, Insects, and the Biomechanics of Flight</I>, a detailed account of our current scientific understanding of the primary aspects of flight in nature.</P><P>Instead of relying on elaborate mathematical equations, Alexander explains the physical basis of flight with sharp prose and clear diagrams. Drawing upon bats, birds, insects, pterosaurs, and even winged seeds, he details the basic operating principles of wings and then moves progressively through more complex modes of animal flight, including gliding, flapping, and maneuvering. In addition to summarizing the latest thinking about flight's energy costs, Alexander presents a holistic view of flight and its ramifications as he explores the ecology and evolution of flying animals, addressing behaviorally important topics such as migration and navigation. With somewhat surprising answers, the author then concludes his study by examining the extent to which natural flight has been inspiring or instructive for the architects of human flight—airplane designers and engineers.</P>