The High Altitude MMIC Sounding Radiometer (HAMSR) is an atmospheric sounder intended for aircraft deployment. It was designed and built at the Jet Propulsion Laboratory under the NASA Instrument Incubator Program and uses advanced technology to achieve excellent performance in a small package. It was first deployed in the field in the 2001 Fourth Convection and Moisture Experiment (CAMEX-4) - a hurricane field campaign organized jointly by NASA and the Hurricane Research Division (HRD) of NOAA in Florida. HAMSR also participated in the Tropical Cloud Systems and Processes (TCSP) hurricane field campaign in Costa Rica in 2005. In both campaigns HAMSR flew as a payload on the NASA high-altitude ER-2 aircraft. It was also one of the payloads in the 2006 NASA African Monsoon Multidisciplinary Activities (NAMMA) field campaign in Cape Verde - this time using the NASA DC-8. Excellent results were obtained in all three campaigns, and the anal-ysis of the data is proceeding. The primary data products generated with HAMSR consist of calibrated brightness temperatures in two tempera-ture sounding bands and one water vapor sounding bands. Derived products include vertical temperature profiles and water vapor and liquid water profiles from the ground to the flight altitude, and experimental products include estimates of precipitation, ice water path and distribution in clouds and above convective cells, and convective intensity. HAMSR provides observations similar to those obtained with microwave sounders currently operating on NASA, NOAA and ESA spacecraft, and this offers an opportunity for valuable comparative analyses.