Just like printed documents, electronic publications must be retrievable in order to be used. Structured descriptive information about electronic documents, so-called metadata, must be mapped to retrieval systems (e.g., library catalogs). Metadata typically are contained in the documents themselves or accessible through them; they must include formal data (author, title, release date etc.) as well as contents-related data (keywords, time and geographic coverage). In addition, the reference system must provide a variety of further information, for instance about modes of access (WWW, telnet, ftp), tools necessary to use the electronic material (e.g., particular software required at the user's site), and computer file characteristics (size, format). The authenticity (identity) of electronic publications needs to be easily recognizable in order to determine which version of the document is being used. Electronic time stamping of documents (i.e., creating a permanent, indelible mark in the digital file that indicates the version), digital watermarking technologies (i.e., software that allows encoding an identification into a document that can be located by WWW search engines), digital fingerprints (i.e., creating hash codes that reflect every bit in a record) and other authentication methods are hoped to help assure the authenticity of electronic publications. Additional information should be available about embedded links to other digital objects, access rights and restrictions, as well as data to prove the integrity of documents.