Renowned researchers from across the globe have contributed significant research inferences in this extensive book. Photonic crystals are described as the periodic optical nanostructures that are designed to affect the motion of photons in a similar way that periodicity of a semiconductor crystal affects the motion of electrons. This book introduces the concepts of innovative systems and materials to the readers. It provides comprehensive information regarding characterization approach of photonic crystal waveguides, photonic crystal lasers as well as plasmonics. Photonic crystal materials have the potential of enabling all-optical computer circuits and can also be utilized to design ultralow-power light sources. There is an in-depth account on lasers from microscopic cavities in photonic crystals acting as reflectors for intensifying the collisions between photons and atoms. This leads to lazing, but these lasers are optically-pumped, meaning that these lasers are themselves driven by other lasers. Furthermore, the physical principles behind the phenomenon of slow light in photonic crystal waveguides, as well as their practical limitations, have also been elucidated. The nature of slow light propagation, its bandwidth restraint, coupling of modes and specific kind terminating photonic crystals with metal surfaces enabling propagation in surface plasmon-polariton waves have also been described. The aim of this book is to provide an analysis of these mentioned issues to provide readers with a better understanding about photonic crystals.