After issuance of the U.S. National Weather Service (NWS) Operational Requirements Document for the next generation Geostationary Operational Environmental Satellite (GOES), in January, 1999, a concept for an imager and sounder to satisfy most of the requirements was developed. The Advanced Baseline Imager (ABI) was initially planned to have 8 channels, with .5 km resolution in the visible channel and 2 km resolution in the infrared (IR) bands. The Advanced Baseline Sounder would be an interferometer, sampling the atmosphere in approximately 1500 narrow spectral bands, with much faster coverage rate than today's sounders. However, as feedback from the user community continued to surface through fora, such as the "Initial GOES-R Series User Workshop", held in Boulder, CO in September of 2000, and the GOES Users' Conference, also held in Boulder, in May 2001, the planned capabilities of the GOES-R Series Imager and Sounder continued to evolve. User recommendations called for a minimum of 12 to 14 imager channels, with 1) calibrated visible channels to be used for cloud detection, aerosol detection, ocean color observations, and vegetative properties; and 2) a variety of IR channels to: detect clouds, determine land and ocean surface temperature, distinguish ice from water clouds, to distinguish clouds from snow cover, detect cloud properties (such as cloud particle size), detect volcanic ash clouds, detect fires/hot spots, just to name a few examples. For a sounder, participants of the GOES Users' Conference recommended it should: 1) provide an accurate three-dimensional picture of atmospheric water vapor; 2) determine atmospheric motions much better by discriminating more levels of motion and assigning heights more accurately; 3) distinguish between ice and water cloud and identify cloud particle size; 4) provide a field of view no greater than 4 km to provide better viewing between clouds and near cloud edges; 5) provide accurate land and sea surface temperatures and characteristics by accounting for the emissivity effects; 6) distinguish atmospheric constituents with improved certainty, including volcanic ash, ozone and methane; and 7) detect atmospheric inversions; 8) provide temperature and moisture profiles within clouds. A microwave sounder, probably on a separate spacecraft would be needed to meet the last requirement To ensure that these and other new instruments meet the needs of a wide cross section of the user community, NESDIS has begun a task of enhancing and unifying the process used to identify, characterize, verify and validate environmental satellite observation requirements. The main components of this process include: 1) a comprehensive, NOAA-wide identification of National Weather Service (NWS), Office of Atmospheric Research (OAR), the National Ocean Service (NOS), and the National Marine Fisheries Service (NMFS) satellite-based, platform-independent, mission requirements; 2) an extensive collection of requirements for both short- and long-term applications across the disciplines of atmosphere, land, ocean, cryosphere and space, including those documented by EUMETSAT and other international agencies; 3) an enhanced process of translating and documenting agency-level mission needs into system-level operational requirements and technology-level acquisition requirements; and 4) extensive cost benefit analysis and validation phases. These efforts should result in establishment of an efficient, cost effective process which solicits, documents, analyzes and updates, from a cost benefit perspective, user requirements for application to the design of current and future satellite systems.