This paper reviews a wide variety of fiber-optic microstructure (FOM) sensors, such as fiber Bragg grating (FBG) sensors, long-period fiber grating (LPFG) sensors, Fabry-Perot interferometer (FPI) sensors, Mach-Zehnder interferometer (MZI) sensors, Michelson interferometer (MI) sensors, and Sagnac interferometer (SI) sensors. Each FOM sensor has been introduced in the terms of structure types, fabrication methods, and their sensing applications. In addition, the sensing characteristics of different structures under the same type of FOM sensor are compared, and the sensing characteristics of the all FOM sensors, including advantages, disadvantages, and main sensing parameters, are summarized. We also discuss the future development of FOM sensors.