This book is a comprehensive study of various aspects related to photonic crystals. It is a compilation of data on diverse theoretical and experimental features of photonic crystals for nanophotonic functions. It deals with various numerical methodologies for the study and design of photonic crystal tools, such as 2D ring resonators for filters, solo and attached nanobeam cavities, birefringence in photonic crystal cavities, threshold study in photonic crystal lasers, vibrant features of photonic crystal filters, among others. The book also discusses numerous features of photonic crystals production and applicable functions, such as nitrogen fault technology in diamond, silicon nitride free standing membranes, photonic crystals arrangements in silicon, photonic crystals for visual sensing, etc. Overall, this book intends to present some useful information for students and experts interested in photonic crystals.