Fiber Optic Gyro (FOG) is an inertial rotation sensor, having a high sensitivity around the earth revolution rate with respect to the sun. Among several configurations of FOGs, Interferometer FOG, which consists of a long length sensing-fiber-coil and interferometric detection scheme, has already been developed well, and created practical applications. Navigation unit in the newest aircraft, Boeing 777, includes 4 I-FOGs.Japanese scientific rockets, M-V and TR-1A, have successfully been launched using navigation equipments with I-FOGs. Ship applications of I-FOG have also been investigated. Beside the traditional applications ofthe gyros, FOGs have additionally created consumer applications, such as car navigation, antenna/camera stabilizer and control/ navigation of radio-controlled helicopters. These new applications could be realized, because of the features of I-FOGs, such as maintenance free and short warm-up time.