Optical fiber sensors are capable of precision measurements across diverse scientific and industrial fields. Their versatility encompasses both point sensors, such as fiber Bragg gratings (FBGs), and distributed sensing techniques. This Special Issue invites manuscripts that introduce recent advances in “Advanced Optical Fiber Sensors for Harsh Environment Applications”. All theoretical, numerical, and experimental papers are welcome. 50' silica multimode fiber (105 mm), Thorlabs low-OH content silica.