Electric strain gauges have been the sensor of choice in structure monitoring applications. Recently, with the invention of fiber optic Bragg gratings and the rapid advance of the telecommunications industry, optical strain sensors based on fiber Bragg grating are increasingly challenging the dominating position of the electric gauges. In this paper, we first discuss the performance and cost issues of typical electric strain sensing systems. This is followed by a description of the operating principles of fiber optic Bragg grating based strain sensors and a new digital spatial and wavelength domain multiplexing (DSWDM) technology for the interrogation of large scale, Bragg grating based sensor arrays. By comparing the performance and costs of electric and fiber Bragg grating based strain sensing technology at system level, we conclude that the fiber optic strain sensing system is not only superior in performance but also provides lower cost per sensor for applications that require more than 35 sensing points. Finally, a number of structure monitoring applications currently under investigation in the Smart Material and Structures Research Laboratory at University of Maryland are presented.