Ranganathan defines the term National Bibliography as "A list of books, periodicals, and of their reprographs published in a country or on the country, or the citizens of the country, or in the language of the country, or written by any citizen of the country irrespective of the country of publication".
Thus, national bibliographies are not necessarily confined to books or printed materials but may bring out national lists of films, records, audio-visuals and other type of non-print material. Depending upon the policy, it may include only one of the above categories or any combination of them.
As publication of a book is a continuous process, a national bibliography may be published weekly, monthly, quarterly, or as fasicules and cumulated at intervals of time ranging from quarterly to yearly or more. Most countries with a book trade, except the United States of America, have some form of national bibliography. They are authoritative and highly reliable sources of information of recorded knowledge of a country. Therefore they serve as excellent selection tools not only for current materials but also good for retrospective materials. The only limitation is that they represent only the national outputs.
British National Bibliography 1950 - Weekly. The British Library Bibliographic Services Division, London. The British National Bibliography (BNB) is a weekly list of newly published books in Great Britain, compiled on the basis of books received by the Copyright Receipt Office of the British Library.
The categories of material excluded are: periodicals, except the first issue of a new periodical and the first issue of a periodical under a new title, music, maps, certain government publications, publications without a British imprint and cheap novelettes, etc.
BNB is in two parts classified and alphabetical. Entries in the classified part are arranged by the Dewey Decimal Classification. The alphabetical part gives the author and subject indexes. BNB is available in print, microforms and in machine readable form.
BNB is a comprehensive and excellent guide for British books. The technical quality its maintenance of international standards in its computerised form, innovative subject index and the general layout and production are examples to follow. BNB is one of the best book selection tools for books with the British imprint.
With the advent of computer networks, national bibliographies of many countries are avail-able online. This enable access to international publications and is an invaluable facility for collection building in large academic and special libraries.