Although health monitoring of civil infrastructures using fiber optic sensing methodology has drawn increasingly attention, the potential of fiber optic sensing in geotechnical engineering is still not well addressed. Fiber Bragg grating (FBG), as the most popular fiber optic sensing technology, has a number of advantages, which make them exceptionally attractive for monitoring physical parameters of geotechnical related structures. This book introduces the recent research and development of FBG technology for the purpose of geotechnical monitoring and stability assessment. A variety of FBG based sensors, including surface glued sensors, tube packaged sensors, embeddable sensing bars, in-place inclinometers, and settlement tubes, have been designed and calibrated. These newly developed FBG sensors were utilized to monitor the deformation and failure mechanisms of laboratory physical models, the pullout behavior of soil nails, the health condition of a mat foundation during construction, and the stability of a newly stabilized slope. Theoretical and numerical analyses have been conducted based on the monitoring results, and the performance of these geo-structures is evaluated.