The fiber gyro, utilizing the Sagnac effect and under development since the early 1980s, has reached production status as a low-cost rotation rate sensor for various high volume applications, satisfied by drift rates of 10°/h and more. Lower drift rates will be offered by series production fiber gyros within the next two years. Principles, technologies and performance data of SEL fiber gyros are discussed, as well as some principal applications. The paper introduces also the concept of a new class of inertial fiber motion sensors based upon the Kennedy-Thorndike interferometer. Such sensors for inertial velocity can enable inertial strapdown navigation without accelerometers.