The UNAVCO Data Center in Boulder, Colorado, archives for preservation and distributes freely accessible high- precision Global Navigation Satellite System (GNSS) data and products to the scientific and education community. The data, which are useful for geodesy, tectonic, volcanological, ice mass, glacial isostatic adjustment, meteorological and other studies, come from 1500 continuously operating stations and 8000 survey- mode observation points around the globe that are operated by over 100 U.S. and international members of the UNAVCO Consortium. These data represent the efforts of individual investigator research projects, large networks such as the NASA Global GNSS Network, the U.S. Geological Survey southern California network, and the very large EarthScope Plate Boundary Observatory that is funded by the U.S. National Science Foundation. By policy, all permanent GNSS station data from UNAVCO are freely available. The Data Center archives, catalogs, and delivers millions of GNSS data products annually. The Data Center also archives for preservation and distributes spaceborne SAR data that are in many ways complementary to the GNSS data collection. SAR data holdings are being acquired in concert with the WInSAR Consortium activities and the GeoEarthScope project and are subject to data distribution restrictions. The metadata for UNAVCO's GNSS data holdings are stored in an Oracle database that supports a rich set of web-based interactions to allow data search, access, and delivery. A metadata exchange with other GNSS data archives has been in place for nearly ten years allowing participants to show each other's holdings as a seamless archive. Efforts are underway to expand and modernize this type of data and metadata exchange through webservices, Open Geospatial Consortium WFS/WMS services, and to maximize the utilization of freely available spatial display technologies such as GoogleEarth. Many users access the UNAVCO GNSS data archives through automated mechanisms that canvas the ftp area for data that are of recurring interest. Station and data discovery mechanisms are available that allow these users to interact with the UNAVCO metadata through an application programming interface (API) with URI requests and XML responses that enhance the user's ability to find and directly download relevant data and metadata in an automated fashion.