Interest in photonic crystals has shown explosive growth in recent years. This interest spawns from the potential for new devices ranging from new optical crossconnects to novel lasers to microstructured optical fiber as well as the possibility of experiments in fundamental physics ranging from enhanced fluorescence lifetimes to atomic traps. All of these applications are made possible not because of the discovery of new physical phenomena, rather through a novel manner of looking at conventional optics. In this talk, I will discuss the theory of these new materials highlighting how relatively simple optical concepts give rise to the exciting properties photonic crystals. I will construct a simple intuitive notion of what defines a photonic crystal and specifically what gives rise to the photonic band gap. Building on this discussion of the physics, I will present our efforts on the realization of two and three dimensional photonic crystals at Bell Laboratories.