The US Environmental Protection Agency (EPA) Terminology Reference System (TRS) has been created to provide a single source of general terminology for the Agency by incorporating EPA-related terms and lists as well as other environmentally-related terminology sources. Terms can be categorized at an organizational and resource level; they are also classified by name and descriptive type. The TRS, currently under development, contains only a few terms, but additional information is being accumulated. Contextual definitions and hierarchical relationships (where they exist) can also be depicted in the TRS.