Abstract: The H2O Antarctica Microwave Stratospheric and Tropospheric Radiometers (Hamstrad) program aims to develop a ground-based microwave radiometer to measure tropospheric water vapor and temperature vertical profiles above the Dome C station, Concordia, Antarctica (75°06'S, 123°21'E, 3233 m above mean sea level, amsl), one of the coldest and driest sites on the Earth. The project intends to study over a time frame greater than ten years the impact of climate change on the budget of atmospheric water vapor (H2O), a major greenhouse gas affecting directly and indirectly (through clouds) the Earth radiative balance. Operating at 60 GHz (dioxygen line to deduce temperature) and at 183 GHz (H2O line), the state-of-the-art radiometer has been installed on site in January 2009 (for 12 days) and is definitively operating since January 2010 after a validation phase at the Pic du Midi station (France) from February to June 2008. Hamstrad measurements can provide vertical profiles of H2Oand temperature from the ground to 10 km above the surface with a time resolution of 7 minutes and a vertical resolution of 30-50 m in the planetary boundary layer, 100 m in the free troposphere and 500 m in the upper troposphere-lower stratosphere. Since the instrument is sampling the diurnal cycle with a good resolution, it can help to validate measurements from spaceborne instruments and meteorological analyses. Systematic comparisons have been performed above Dome C with measurements from in situ sensors, radiosondes, spaceborne instruments such as the Infrared Atmospheric Sounder Interferometer (IASI) onboard the MetOp-A platform and the Atmospheric InfraRed Sounder (AIRS) onboard the Aqua plateform together with the analyses from the European Centre for Mediumrange Weather Forecast (ECMWF). Temperature and absolute humidity measurements fromHamstrad are of a great quality in the planetary boundary layer, degrading in the free troposphere to lose sensitivity in the upper troposphere-lower stratosphere.