020 ISBN

ISBN stands for International Standard Book Number and these numbers will be found in 020 tags in the MARC record. It is a repeatable field and each individual ISBN assigned to a publication gets its own 020 tag.

The ISBN Standard (which is an ISO standard) was first published in 1972 and there are currently more than 150 ISBN registration agencies providing ISBNs for publishers in 200+ countries around the world. Bowker is the ISBN registration agency for the United States. To be sure that ISBNs issued by different agencies are unique throughout the world, the International ISBN Agency assigns unique group prefixes and ranges to each ISBN registration agency.

ISBNs are calculated using a specific mathematical formula and include a check digit at the end to validate the number. Until the end of 2006 ISBNs were 10 digits long but are now 13 digits and begin with either 978 or 979. Ten-digit ISBNs can be converted to 13-digits and 13-digit ones starting with 978 can be converted to 10s but ISBNs beginning with 979 exist solely in 13-digit form. Where conversion is possible you may see both versions in separate 020s as that is OCLC's policy.

If you want to know exactly what all the digits in an ISBN mean check out "What is an ISBN?".  ISBNs printed in books often include hyphens between the various parts which should always be omitted from the number in the 020 tag. 

There are 3 subfields that you will find in current 020 tags:

• subfield a contains the ISBN
• subfield z contains invalid or cancelled ISBNs
• subfield q, if it is present, contains "qualifying information"

"Qualifying information" is a statement about the item associated with the number recorded in subfields a or z. Prior to 2013, when this subfield was defined, qualifying information was contained in subfield a and subfield z. Here are a few examples of "qualifying information":

020 _ _ ǂa 0893571121 ǂq (pbk. ; ǂq v. 1)

020 _ _ ǂa 9781100216249 ǂq (electronic bk.)

020 _ _ ǂa 0061435163 ǂq (sound recording. ; ǂq OverDrive Audio Book)

020 _ _ ǂz 9780702053351 ǂq (paperback)

Older records may also include data about the terms of availability (prices and such) in a subfield c. This is no longer a valid 020 subfield except to indicate rental material in cataloging records for musical scores.