This book is aimed at students and researchers who wish to use reflectance and emittance as quantitative tools to measure the properties of surfaces and materials. It is intended primarily for use in the interpretation of remote observations of the surfaces of the Earth and other planets, and it will also be useful to chemists, physicists, geologists, engineers and others who deal with particulate media. Topics include propagation and absorption of light in continuous media, reflection by smooth surfaces, scattering by spheres and irregular particles, reflectances and emissivities of particulate media, reflectance and emittance spectroscopy, and the polarization of light scattered by particulate media. Many examples of applications are given.