This chapter presents a review of the most recent developments in the technology of fiber optic sensors as well as some of their applications in monitoring the performance of civil infrastructure such as buildings, bridges, sidewalks, dams, tunnels and piles. It discusses the most prominent current problems faced by fiber optic sensors with their applications to monitor civil structural performance. The fiber optic sensor is either compactly or superficially anchored to various materials, such as concrete, reinforcing steel, steel sheets, fiber reinforced polymer strips, and others. The corrosion of steel cables and reinforcing steel in concrete represents one of the leading causes of durability problems affecting civil infrastructures. When external force or compression is applied to fibers, the fibers bend over small semicircular filaments, thus breaking the center light of the fiber from the heart to the protective fiber layers, causing a decrease in light intensity.