The National Aeronautics and Space Administration (NASA), in coopera- tion with the Japan Aerospace Exploration Agency (JAXA), launched the Tropi- cal Rainfall Measuring Mission (TRMM) in 1997. Designed as a minimum three- year mission with the goal of five years duration, TRMM has been collecting data for seven years, in large part due to the reliability of its sensors and the high quality of their measurements. Although initially intended as a purely research- oriented mission, TRMM now is used in operational applications such as hurri- cane forecasting because data from its suite of complementary sensors are unique and available in near real time. In the United States TRMM data are used opera- tionally by the Joint Typhoon Warning Center, the National Center for Environ- mental Prediction, and the National Hurricane Center, among others. Interna- tionally the data are used operationally by entities such as JAXA, the European Centre for Medium-Range Weather Forecasts, and the World Meteorological Organization tropical cyclone warning centers.