Plant leaves collectively represent the largest above-ground surface area of plant material in virtually all environments. Their optical properties determine where and how energy and gas exchange occurs, which in turn drives the energy budget of the planet, and defines its ecology and habitability. This book reviews the state-of-the-art research on leaf optics. Topics covered include leaf traits, the anatomy and structure of leaves, leaf colour, biophysics and spectroscopy, radiometry, radiative transfer models, and remote and proximal sensing. A physical approach is emphasised throughout, providing the necessary foundations in physics, chemistry and biology to make the context accessible to readers from various subject backgrounds. It is a valuable resource for advanced students, researchers and government agency practitioners in remote sensing, plant physiology, ecology, resource management and conservation.