The 21 September 1999 marked the launch of WebVoyager, the HTTP interface for access to Voyager, the new Library of Congress catalogue. This article describes the characteristics and peculiarities of the new OPAC, its contents and access modalities (available interfaces), making comparisons with the old system on IBM mainframe, LOCIS (Library of Congress Information Systems), which closed on 12 August 1999. Voyager contains almost 12 million records for monographic works, serials, computer files, manuscripts, cartographic material, sound and video material, including the over 4.7 million records from the PREMARC file. At the moment Voyager includes information from more files than the old LOCIS system. The BOOKS files (LOC1, LOC2 and LOC3) include the materials catalogued from 1898 to 1975. With respect to the old LOCIS, Voyager does not include records from other research libraries and records from bibliographies and data bases for materials not held at the Library of Congress. LOCIS "aggregated" the old systems that were separated from one another, with over 30 different files, some of which dated to the end of the Sixties, or the beginning of the Seventies. The Library of Congress decided to break up and locate outside the boundaries of the new OPAC much of that material which was previously described within the catalogue. That material can be accessed from the LC Web site in an integrated way to the OPAC; for example the old Copyright file produced by the Copyright Office, which include bibliographic records and information for documents from 1978 to the present day, can now be consulted from the set of Web pages available on the site; the same is true for the GPO (Government Printing Office) documents, the legal documents and the photographic collections on American memory. The records from the files that include Braille and audio material can be accessed from the Web-BNLD catalog on the LC site of the National Service for the Blind and Physically Handicapped. The catalogue includes over 2700 electronic volumes in Braille, recently placed on the net for users authorized to access the National Service for the Blind and Physically Handicapped. The new OPAC can be accessed, as well as from WebVoyager, also through Z39.50 in two ways, simple (keyword) and advanced (with the use of Boolean operators), and in just a textual way (ASCII) of the telnet type. The search and browse capabilities offered by the new OPAC Web are numerous, Subject Browse, Name Browse, Title, Serial Title, Call Number Browse, Guided Keyword, Command Keyword, Keyword, grouped into four modalities: Subject-Name-Title-Call#, Guided Keyword, Command Keyword, Keyword. There are four possible choices for the display of the record: Brief Record, Subject/Content, Full Record, MARC Tag. Various also are the functions available that make the new OPAC a flexible and refined instrument: Limiting Searches, Search History, Boolean Searching, with the offer of a complete set of tools for the refinement of the search, including the use of Boolean operators of specific codes for searching in indexes, of various filters for limiting the search, and a powerful system of relevance ranking to evaluate the items retrieved. Copies of the bibliographic records can be printed, saved or sent to a postal mailbox, one record at a time or as a whole set. Many help screens can be reached from various points of the catalogue and from various search or browse modes.