This dataset contains Level 1c inter-calibrated brightness temperatures from the Advanced Microwave Sounding Unit-A (AMSU-A) sensors onboard six polar orbiting satellites (NOAA-15, -16, -17, -18, EUMETSAT MetOp-A, and NASA Aqua) spanning from 1998 to the present. The dataset was produced by the NOAA Center for Satellite Applications and Research (STAR), and is a Fundamental Climate Data Record (FCDR) of microwave brightness temperature in the NOAA CDR Program. AMSU-A is a 15-channel microwave radiometer with a ground spatial resolution of about 50 km in diameter at nadir. The native AMSU-A Level 1b data were inter-calibrated using the Integrated Microwave Inter-Calibration Approach (IMICA) method to obtain a long-term data product to be used in climate analyses. For comparison, data files also include the operational data used in NWP forecasting along with the IMICA calibrated radiances, which minimize or remove the biases found in the operational calibration. In addition, limb adjusted radiances for both the IMICA and operational calibrations are included for certain type of climate applications, such as atmospheric layer temperature development using the radiance datasets. The orbital swath data files include AMSU-A channels 4 through 14 (between 52.8 and 57.6 GHz) for both the IMICA calibration and the operational calibration. The inter-calibrated AMSU-A data may be updated as the sounding units are further calibrated over time. In early 2017, a gridded version of the dataset was made available to the public. There are three types of gridding approaches: brightness temperatures of near-nadir Field of View (FOV) only, brightness temperature of FOV with minimum viewing zenith angle, and average brightness temperatures of FOVs from multiple scan positions.The gridded data are the produced using the same methodologies as the swath data, but are calculated to a 1x1 degree grid resolution with global coverage.