Fiber Bragg Gratings (FBGs) have quickly established themselves as one of the key enabling technologies behind the 'DWDM Revolution'. EDFA gain-equalising filters, WDMs and add-drop multiplexers, created as periodic variations in the refractive index of the core of the fiber itself, have all played their part in delivering almost unlimited bandwidth - and in accelerating the transition of the entire telecommunications industry from a digital electronic to a digital photonic world. FBGs can also be used in the fabrication of optical strain and temperature sensors, with quasi-distributed measurements possible using gratings written sequentially into a continuous length of fiber.