Since the 1970s, the interferometric fiber-optic gyroscope (IFOG) technology based on the Sagnac effect, which boasts unique advantages, has developed rapidly with the increasing application and maturity of optical devices such as optical fibers, light sources, and phase modulators in optical communication. Over the past 40 years, this technology has moved from the laboratory to various practical fields such as land, sea, air, and space. This paper reviews the recent development of the IFOG technology. Firstly, the exploration process of this technology from the birth of the Sagnac effect to its practical applications is introduced. Secondly, the classical minimum reciprocity configuration of IFOGs and the signal processing scheme are described. Then, the research status of this technology in high precision, miniaturization, and application environment adaptability is summarized. Finally, the development and application trends of this technology are analyzed.