Presently, advanced fiber optic sensor development centers upon interferometric or polarization modulated sensing techniques that make use of the high sensitivity achievable only through single mode waveguiding. Each sensing application incorporates a very specialized single mode fiber in order to meet the sensor's specific fiber requirements. These specialized single mode fibers, being much different than standard telecommunication single mode fiber, present challenges to fiber designers and manufacturers. As this technology matures, certain fiber types are becoming standardized for specific sensing applications. An overview of these single mode fibers will be presented along with the effect of fiber coatings relevant to the sensor performance. A brief discussion on future trends in development of single mode fibers for intrinsic sensing applications will also be included.