Web geographic information systems (GISs) and the Internet are now providing the connectivity necessary to support large-scale data access by a wide variety of users, including not just scientific researchers, but also policy-makers and marine resource managers. However, connectivity alone cannot ensure that those who need natural resource information will be able to locate relevant data. Data clearinghouses need to provide user interfaces that help a broad user community understand what spatial data are available, how they can be obtained, and how they should be interpreted. The Metadata Humane Society project conducted by researchers at Oregon State University combined traditional interface engineering knowledge, scientific research and geographic information science (www.nacse.org/mhs). The researchers wanted to improve access to spatial information by identifying the primary barriers to usability for the National Geospatial Data Clearinghouse (NGDC) interfaces. The project included developing an understanding of the current state of usability among GIS-related Web sites that provide metadata search facilities and identifying promising approaches to “learnability” and navigability that might be exploited in improving the NGDC interfaces. To accomplish these 3 goals, three types of usability evaluations were performed: initial predictive evaluation of existing sites, user testing of existing NGDC Interface, and a user expectations survey. The evaluations involved actual users from a range of disciplinary backgrounds and user communities, as well different levels of expertise. The project found that different levels of user expertise require distinct subsets of the usability criteria. It is recommended that there be at least two interfaces available for the NGDC addressing different target audiences, and that each interface should focus on certain criteria. To improve the delivery of spatial information to marine resource managers, these recommendations to increase usability should be applied to data clearinghouses such as the Virtual Oregon, Oregon Coast Geospatial Clearinghouse and the Geography Network.