Fiber Bragg grating (FBG) is inherently sensitive to temperature and strain. By modulating FBG’s strain, various FBG sensors have been developed, such as sensors with enhanced or reduced temperature sensitivity, strain/displacement sensors, inclinometers, accelerometers, pressure meters, and magnetic field meters. This paper reviews the strain modulation methods used in these FBG sensors and categorizes them according to whether the strain of an FBG is changed evenly. Then, those even-strain-change methods are subcategorized into (1) attaching/embedding an FBG throughout to a base and (2) fixing the two ends of an FBG and (2.1) changing the distance between the two ends or (2.2) bending the FBG by applying a transverse force at the middle of the FBG. This review shows that the methods of “fixing the two ends” are prominent because of the advantages of large tunability and frequency modulation.