Optical fiber sensors [1-5] are devices for which a physical, chemical, biological, or other measurand alters the properties of the light guided in an optical fiber (an intrinsic sensor) or guided to and from an interaction region (extrinsic sensor) by an optical fiber and leads to the generation of an optical signal related to the measurand. ™is optical signal then ultimately generates a current in a detector. ™e optical information is conveyed by a change of phase, polarization, frequency, intensity, or a combination thereof. ™e operation of sensing using phase, polarization, or frequency modulation involves interferometric or grating-based signal processing. ™e intensity-based sensor is the simpler sensor but is much less sensitive than the interferometric sensor. ™e relevant measurands can be temperature, stress, strain, pressure, vibration, position, humidity, viscosity, rotation, acceleration, electrical currents, electric and magnetic fields, and bio-attachment molecules. Some attractive reasons for using optical fiber sensors include small sizes, light weight, immunity to electromagnetic interference (EMI), high-temperature performance, environmental ruggedness, large bandwidth, distributive sensing, easy space, time, frequency, and polarization multiplexing. ™ey can also operate over very long distances. Optical fiber sensors are chemically and biologically inert since the basic sensor material, silica, is unaffected by most chemical and many biological agents. Even though strain, temperature, and pressure have been the most widely studied measurands, applications of fiber sensors in biology have been gaining traction in the last several years and several new applications of these sensors have emerged. Fiber Bragg grating (FBG) sensors are sensors based on an inscribed grating at the core of a fiber. As we will see, they can be seen as stable interferometric sensors. Over the last 10 years, because of their ease of fabrication, use, and good sensitivity, they have become one of the most popular topics in optical fiber sensors.