There is often confusion over the meaning and usage of terms such as efficiency, economy, effectiveness, optimization and perfection in biology. This book defines and discusses these concepts within a broad evolutionary perspective and considers how evolutionary pressures can affect the economy and efficiency of animals. Chapters consider biomaterials, skeletal systems, muscular function, aquatic and terrestrial locomotion, and cardiovascular systems. The result is a book of interest to all biologists, particularly those working in the field of comparative physiology and evolutionary biology.