With the possible exception of nonsilica glasses, each time a new fiber technology has emerged, someone has applied it to FOGs and reported beneficial results. The development of the FOG has essentially tracked that of commercial optical fibers for more than 40 years, running parallel since 1976, when Vali and Shorthill first demonstrated the concepts originally proposed by Pircher and Hepner in early 1967. The nine-year gap between first proposal and experimental demonstration was undoubtedly caused because, in 1967 practical, single-mode fibers simply did not exist, and even by 1976 they were in their infancy and confined to a handful of research laboratories around the globe. FOG technology received a further boost at the beginning of the 1980s when stress-birefringent polarization-maintaining (PM) fibers were developed almost simultaneously by multiple commercial and academic institutions, including NTT, Corning, Hitachi, Bell Laboratories, and the University of Southampton. It was the advent of PM fibers that paved the way for commercial FOG development by delivering practical immunity to environmental variations such as vibration and temperature. To this day, precisionwound coils of PM fiber dominate the FOG industry. Nevertheless, with FOG technology challenging the ring laser gyro (RLG) in navigation-grade sensors and even making in-roads into strategic levels of precision, virtually every new development in fiber technology has been investigated extensively to discover if theoretical performance advantages in FOGs may be realized.