Many data sets used by EPA's Environmental Monitoring and Assessment Program (EMAP) will be collected and managed by groups other than EPA as the Committee on Environment and Natural Resources develops the inter-agency National Environmental Monitoring Initiative. Managing these data requires a change from a database managed solely by EPA to a model where there is, in addition to distributed databases, truly distributed ownership and responsibility. Common standards, data directories, and data descriptions allow data of interest to be located, understood, and downloaded. The level of EMAP data management practices applied to a data set is based on the degree of EMAP responsibility for the data. The EMAP Data Directory is an Oracle database that tracks data sets of interest and contains sufficient information about a data set for a user to determine if the data are of interest. Some of the data sets listed in the Directory are in the possession of EMAP and are accessible on the EMAP WWW site (http://www.epa.gov/emap). Other data sets in the Directory are managed, documented, and made available by other organizations. The Data Catalog contains metadata about data sets in the possession of EMAP and provides the user with information about methods, assumptions, and data quality.