An environmental library system (ELS) for the United States Department of Housing and Urban Development has been developed and installed in six HUD offices to bring together all nationwide and local environmental source materials in an information system with comprehensive cataloging and computer-assisted access. The accompanying manuals indicating how to use the various sources needed to answer environmental questions comprise one of the basic elements of the system, which also includes question guides, the collection itself, and a card catalog. (Author/JVP)