Organized from analytical to computational methods, this book discusses the electromagnetic-theoretical methods that can be effectively applied to modeling photonic crystals and related optical devices. This book introduces and describes each method, presenting detailed formulations for practical applications. These methods include scattering matrix, multipole theory of scattering, model of layered periodic arrays for photonic crystals, the multiple multipole program, mode-matching, the finite-difference frequency-domain technique, and the finite-difference time-domain method. This text provides a comprehensive reference for professionals working in this field.