Of all the water on the Earth, only 3% is drinkable and two thirds of that water is locked away in polar ice. Precipitation constantly renews our fresh water resources and the latent heat it releases is the principal source of energy that drives atmospheric circulation and weather disturbances. It is the principal indicator of the rate of global water cycle and can also be used effectively as input for numerical weather forecasting. The Global Precipitation Measurement (GPM), a cooperative effort of the National Aeronautics and Space Administration (NASA) and Japan's National Space Development Agency (NASDA), aims to gather precipitation and related data globally. It will build upon the legacy of the extremely successful Tropical Rainfall Measuring Mission and will extend the spatial and temporal coverage of precipitation measurement to identify trends in the Earth's global water cycle, further explore the structure of rainfall to improve efforts to predict climate, and provide high quality rainfall accumulation products. GPM envisions a core satellite, up to eight constellation satellites, local ground validation sites and regional high quality rain gauge networks, and a global precipitation data system. It is anticipated that NASDA will provide the core satellite's dual frequency precipitation radar, its launch vehicle, and a constellation satellite. GPM's flexible architecture enables other international and domestic participants to provide enhancements incrementally as plans permit. The European Space Agency (ESA) is currently studying contribution satellite, EGPM, as an Earth Explorer Opportunity Mission. GPM is now in the Formulation Phase and is one of the highest priorities among the new missions for which NASA's Earth Science Enterprise seeks final approval. GPM launches are targeted to begin in 2007.