The Operational Land Imager (OLI) on Landsat-8 has been collecting imagery on orbit for 17 months. The radiometric performance of the OLI is monitored using on-board systems (lamps and solar diffusers) as well as by reference to lunar and ground measurements and other satellite systems. Over this nearly 1a1/2 years of operation the OLI has been extremely radiometrically stable in all of its 9 spectral bands. Only the shortest wavelength band, centered at 443 nm, which has degraded about 0.8%, has changed by more than the variability among the measurements (0.2%). This consistency between the lamps, diffusers, moon, and ground measurements lends high confidence to these statements, which is unusual for a system so early in its lifetime. Comparisons to other satellite systems and ground measurements show that the OLI is calibrated to within requirements and generally better than 3% in both radiance and reflectance.