This lecture describes the use of single mode optical fibers as a means of sensing temperature and strain measurands. By interrogating the intensities of the backscattered spontaneous Brillouin and Rayleigh signals generated by a pump, one can obtain temperature and strain information distributed along the fiber. The lecture also describes the opto-electronic components of this distributed sensor such as the laser sources, optical filters and a cascaded optical filter system that can decouple the Brillouin intensity and frequency information.