Photonic crystals (PCs) have many fascinating optical characteristics. Photonic crystal waveguides (PCWs) and PCW-based devices are rapidly being proposed, designed, and simulated due to their small device size. Similar with PCWs, periodic dielectric waveguides (PDWs) are also waveguides in periodic medium. Compared with PCWs, periodic dielectric waveguides (PDWs) are considered newcomers. Attributed to the fact that the optical field is confined in the periodic dielectric rather than in the defect of the PCWs, PDW-based devices will be even smaller and much simpler than the PCW-based devices. This book examines self-imaging phenomena in PCWs and PDWs, as well as a discussion of a number of passive devices designed in silicon-based PCWs and/or PDWs.