The National Oceanographic and Atmospheric Administration (NOAA) is now considering a microwave radiometer for the new series of Geostationary Operational Environmental Satellites (GOES) to be launched starting in 2012. GOES-R is expected to begin operations around 2014 and will provide significant advances in Earth coverage, environmental data, and prediction capabilities. GOES' unique vantage point in fixed geostationary orbit provides continuous, near-real-time updates (observations) of weather and environmental conditions for the Americas and large portions of the Atlantic and Pacific Oceans. In general, GOES-R sensor improvements arise from more frequent updates, finer spatial/spectral resolution, and an expanded field of view. Infrared (IR) atmospheric sounders are designed to provide excellent observations in clear conditions. Critical information within clouds and under cloud cover, however, is not available in the IR spectrum. Microwave sounders can provide synergistic coverage by their ability to observe energy through clouds. NASA's Earth Observing System (EOS) AQUA with the Advanced Microwave Sounder Unit (AMSU) and Atmospheric IR Sounder (AIRS) has illustrated the benefits of combining infrared and microwave sounder data. The benefits provided by polar microwave sounders can be extended to geostationary satellites. The combination of the Hyperspectral Environmental Suite (HES) IR sounder and Geostationary Microwave Sounder (GMS) can likewise provide complete geostationary sounder coverage and precipitation measurements.through our hemisphere. Three different sounders designs have been proposed for the GOES-R Geostationary Microwave Sounder (GMS); these designs would all use similar frequency bands to those of the AMSU A and B and therefore benefit from existing retrieval algorithms. Two designs use mechanically steered solid dish antennae, while a third design utilizes a sparse aperture antenna technology. All three GMS designs take advantage of the latest developments in sensor technology, algorithms, and antenna design. The joint NOAA/NASA GOES-R Program Office (GPO) is evaluating the various GMS designs for GOES-R. This paper will address the design, status, and advantages and limitations of these GMS approaches in reference to unmet meteorological requirements as part of Pre-Planned Product Improvement (P3I) on the GOES-R series of satellites.