The textbook "Nonlinear Photonic Crystals" offers a comprehensive examination of the nonlinear optical properties of periodic dielectric structures. Over the past two decades, the field of research has rapidly evolved, particularly due to new manufacturing techniques that enable the production of fiber gratings and multidimensional photonic crystals. These materials are characterized by their ability to vary the refractive index through light pulses. The book discusses novel phenomena such as gap solitons, which can move at variable speeds, as well as spatial solitons that prevent the diffractive spreading of light in waveguide arrangements. Additionally, the role of microstructured optical fibers is highlighted, which allow for targeted control of guided mode dispersion for the generation of broadband light. The topics covered are of great significance for the development of new optical devices, especially in the fields of optical communication and data processing.