Surface emissivity is essential for deriving the surface skin temperature from satellite-based infrared measurements. It is also critical for determining thresholds for cloud detection and for estimating the emission of longwave radiation from the surface, an important component of the energy budget of the surface-atmosphere interface. In this paper, simultaneous data from satellite imagers taken at 3.7, 10.8, and 12.0 µm are used to simultaneously derive the skin temperature and the surface emissivities at the same wavelengths. The methodology uses separate measurements of the clear-sky temperatures in each channel during the daytime and at night. The relationships between the various channels at night are used during the day when solar reflectance affects the 3.7-µm data. A set of simultaneous equations are then solved to derive the emissivities. Global results are derived from Advanced Very High Resolution Radiometer data while GOES-8 data are analyzed to examine the diurnal variation of this parameter over a mesoscale domain centered on the Atmospheric Radiation Measurement Program central facility in Northern Oklahoma. Numerical weather analyses are used to provide soundings for correcting the observed radiances for atmospheric absorption. Seasonal averages are computed a range of surface vegetation types. These results are made available for remote sensing and other applications.