There is currently no active, single-ended optical technique for remotely sensing the refractive index structure characteristic Cn2 in the turbulent atmosphere. A capability to remotely measure Cn2 is needed in several areas. In astronomy, the vertical profile Cn2(h) is required in order to understand and improve the performance of adaptive optics systems, and measurements of Cn2 in arbitrary directions above fixed points on the ground would be useful in site surveys. Researchers in basic atmospheric physics need an optical technique because it would be sensitive to temperature fluctuations only and not water vapor fluctuations, unlike the radar and acoustic sounders which are currently used. Understanding laser beam degradation, for communications, power beaming, or weapon system development, also requires a knowledge of Cn2. An optical remote sensor for Cn2 could also be used for horizontal, path-averaged measurements, to infer fluxes of heat and momentum over land or sea surfaces. We have recently proposed three different lidar-type techniques for remote sensing of Cn2, based on the following phenomena: enhanced backscattering, residual turbulent scintillation, and image distortion. Each of these techniques is reviewed here in terms of its advantages and disadvantages for various applications, and some considerations for practical systems are also discussed.