Within the past several years “photonic crystals” have emerged as a new class of materials providing new possibilities for the control and manipulation of light. These materials are viewed ideally as a composite of a periodic array of macroscopic dielectric or metallic scatterers in a homogeneous dielectric matrix. A photonic crystal affects the properties of a photon in much the same way that a semiconductor affects the properties of an electron. Consequently, photons in photonic crystals can have band structures, localized defect modes, surface modes, etc. This new ability to mold and guide light leads naturally to many novel phenomena associated with light. ©2001 American Institute of Physics.