The Tropical Rainfall Measuring Mission (TRMM) Ground Validation (GV) Program began in the late 1980’s and has provided a wealth of data and resources for validating TRMM satellite estimates, especially at Kwajalein, Republic of the Marshall Islands, and Melbourne, Florida. The TRMM GV program has provided a full data set (1998-present) of GV products at both sites, which compares well with TRMM estimates (within 10% over open ocean). With the advent of the TRMM Version 6 satellite products, there has been a convergence of both intra-satellite estimates (Precipitation Radar (PR), TRMM Microwave Imager (TMI) and Combined (COM)) algorithms and GV. As the TRMM mission winds down, with the eventual atmospheric re-entry of the satellite, focus has begun towards planning for the Global Precipitation Measurement (GPM) GV program. While the main goal of TRMM GV was to provide validation of surface precipitation (rates and accumulations), the main objectives of the GV program are fourfold: (1) to quantitatively assess the error in space-borne precipitation retrievals; (2) to diagnose the sources of space-borne retrieval error; (3) to suggest improvements to the space-borne algorithms to reduce retrieval error; and, (4) to provide quantitative evaluation and improvement of the techniques and algorithms employed in ground validation. This paper describes how TRMM GV data is being used to develop the tools to meet these GPM GV objectives.