Biomechanics has emerged in the past twenty years as a burgeoning enterprise that integrates approaches from engineering with studies of animal function. With over 35,000 species, fishes are the largest clade of vertebrates and demonstrate remarkable diversity in body form, ecology, behavior, and physiology. Fishes are critical components of the earth's environment and understanding how fishes function is essential for future advances in conservation and fisheries biology, understanding major patterns in the evolution of fishes, and in the construction of new underwater robots based on the principles of fish functional design. In Fish Biomechanics, leading workers in the area of biomechanics review major functional systems in fishes, and provide an overview of new approaches and techniques that are allowing long-standing questions about fish functional design to be addressed. Chapters are written to allow the non-specialist in biomechanics to understand the approaches and concepts that underlie the remarkable recent advances in our understanding of fish respiration, locomotion, prey capture, physiology, and sensing of the environment.