Civil structures and infrastructure are inevitably subjected to damage and deterioration caused by natural or man-made events or processes. Thus, sustainable preservation, maintenance, renewal, and repurposing of civil structures and infrastructure is becoming a key challenge in modern society. Structural Health Monitoring (SHM) is a process aimed at providing actionable information on structural health condition and performance, which in turn can be used to plan and optimize the remedial actions relative to above presented challenge. Development of Fiber Optic Strain Sensors (FOSS) played an important role in establishing SHM as a viable solution for evaluation of structures, applicable in real-life settings. They brought two strengths into the area: excellent long-term performance in terms of stability and reliability and two unprecedented sensor types: long-gauge and truly distributed sensors. This paper briefly summarizes physical principles of selected FOSS, introduces SHM approaches specifically enabled by long-gauge FOSS, and demonstrates their effectiveness through real-life applications.