High spectral resolution polar-orbiting satellite instruments, such as AIRS and IASI, can be used to intercalibrate the global system of operational geostationary imagers. The international community of satellite operators, through the WMO, has recognized a need for an improved quantitative assessment of satellite calibration for applications such as climate monitoring and has formed an international committee to coordinate a Global Satellite-Based Intercalibration System (GSICS). In addition to climate monitoring, intercalibration provides satellite operators with near real time feedback on instrument operation and response to changes implemented from the ground. Comparisons between geostationary imagers and the high spectral-resolution Atmospheric InfraRed Sounder (AIRS), polar-orbiting on Aqua, have provided an accurate estimate of calibration performance of the world's geostationary imagers. AIRS has been proven to have absolute calibration accuracies of 0.1K in most bands. However, AIRS does not have complete spectral coverage. The channels on geostationary imagers where AIRS has spectral gaps, such as the water-vapor absorption region, are difficult to compare accurately. IASI, which does not have spectral gaps, offers another opportunity for geostationary satellite intercalibration as well as validation of spectral interpolation techniques being used for AIRS where necessary. Both AIRS and IASI are being used to intercalibrate the world's geostationary imagers.