Optical-fiber sensors are emerging as a superior non-destructive means for evaluating the condition of concrete structures. In contrast to existing non-destructive evaluation techniques, optical fibers are able to detect minute variations in structural conditions through remote measurements. Structures fully integrated with optical fibers will be able to monitor the initiation and progress of various mechanical or environmentally-induced degradations in concrete elements. Recent advances in fiber-optic sensor technology and the possibility of their use in concrete structures have instigated the development of a number of research activities. Owing to inherent interdisciplinary nature of the field of fiber optics, the expertise of the researchers active in the research and development of fiber-optic sensors covers a wide spectrum of disciplines including concrete engineering, as well as opto-electronics and physics. This article is intended for rapid dissemination of the current state-of-the-art in this emerging technology. However, because of the interdisciplinary nature of the subject, a brief discussion on the physical nature of optical fibers is also presented.