This second edition is completely revised and improved and contains eight new chapters and six new appendixes. In addition to the theoretical background on light propagation through diffusive media, this update also provides new didactical material, including: A comprehensive statistical approach to the photon penetration depth in diffusive media. An introduction to anomalous transport. An anisotropic transport approach within the framework of diffusion theory. An introduction to the invariance properties of radiative transfer in non-absorbing media. A heuristic explanation of ballistic photon propagation. An expanded description of core Monte Carlo simulation methods. A series of new analytical solutions of the diffusion equation for new geometries. Some original solutions in the time domain of the diffusion equation in the presence of Raman and fluorescence interactions. New MATLAB (R) codes of the presented solutions. A revised and enlarged set of numerical Monte Carlo results for verification of the presented solutions. An augmented bibliography covering the field of tissue optics. Although the theoretical and computational tools provided in this book have their primary use in the field of biomedical optics, there are many other applications in which they can be used, including, for example, analysis of agricultural products, study of forest canopies or clouds, and quality control of industrial food, plastic materials, or pharmaceutical products, among many others.