This lecture covers the fundamentals and applications of Fiber Bragg Gratings (FBG), which are periodic or aperiodic perturbations of the refractive index in the core of an optical fiber. The FBG fabrication process, spectral response, and different types of FBGs such as chirped and apodized gratings are discussed. The compensation of group velocity dispersion using chirped FBGs and the concept of optical phase conjugation for dispersion compensation are explained. The lecture also addresses the limitations imposed by attenuation and dispersion on the maximum transmission length in optical fiber communication systems.