MARC21 bibliographic records - 020 tag

The ISBN is a 13-digit or 10-digit publisher assigned number and is assigned to various types of material including books, visual materials and sound recordings, etc. In a perfect world, each ISBN would be unique. Unfortunately, numbers can be, and are erroneously assigned to multiple books by the publishers, or recycled from an item no longer in print. The 020 tag in MARC21 bibliographic record has no indicators and contains the ISBN (International Standard Book Number). The ISBN is found in subfield 'a' the indicator for which is implied and does not appear on the record. On occasion, you may find an ISBN preceded with a ‡z (subfield z). This indicates that the ISBN listed in that subfield is not valid. Another sub field code that is optional, but may be found in the 020 tag, is ‡c Terms of availability and most typically would list the price of the item.

Each ISBN has four parts: the language group of the country of publication, the publisher's identifier, the title number, and a check digit. The 13-digit number differs from the 10-digit number not only by the 978 (979 for other locales) which begins all of the 13-digit numbers, but also by the formula calculated check digit at the end (numbers 0 through 9, or the letter x) . Therefore you cannot drop the 978 from a 13-digit ISBN as a shortcut to the 10-digit number. For example 9780312626686 and 0312626681 for the same record are different from one another. Likewise, you cannot drop the beginning zero/s from a 10-digit ISBN or the ending check digit 'x' from either number.

When printed in a book, an ISBN may appear hyphenated separating the four parts; but you should not use the hyphens when searching (or creating) a record. Each ISBN appears in it's own 020 tag, so do not type both the 13-digit and the 10-digit ISBN into a search box and expect a valid result. You must search by either one or the other. If a book appears in both hard cover and paperback editions, and if the publishers are the same, both ISBNs may be found in separate 020 fields of the same record. In the case of books, you may find the ISBN located on the back of the title page, on the back cover of the book or on the dust jacket if there is one. (NOTE: When a book has been rebound, an ISBN may be found on the back cover of the book that differs from the one found on the title page verso. The correct ISBN to use to identify the material would be the one found on the title page verso.) On materials other than books, the ISBN is normally found on the packaging.

ISBN searching is an easy way to find records in NHU-PAC and is an excellent place to start. If you don't find a match by ISBN, there may still be a matching record in the database for your item, so you should try another search (title or author are good choices) before assuming no record is available.