A taxonomy of 11 sources of information used during library and database searching is presented, based on observation of 49 searches in a variety of libraries and search situations. Three broad categories of sources are identified: those internal to the searcher; those created by the searcher; and those external to the searcher. Internal sources are reason for the search, necessary beliefs, object of the search, object knowledge, domain knowledge, and search knowledge.Two sources created by the searcher are expressed object and searcher terms. External sources of information that are encountered in the search environment are guidance devices, system terms, and the collection. Found object, a subset of the collection, is also what is taken away from the library or IR system.