022 ISSN

ISSN stands for International Standard Serial Number and these numbers will be found in 022 tags in the MARC record. It is a repeatable field, but I have rarely seen a record with more than one 022 in it.

An ISSN is an 8-digit code used to identify newspapers, journals, magazines and periodicals of all kinds and on all media–print and electronic. The version published in each type of media is assigned a separate ISSN. To learn more about how they are assigned and kept track of check out "Understanding the ISSN". For serials published in the United States ISSNs are assigned by the U.S. ISSN Center in the Library of Congress.  

There are multiple subfields defined for the 022 tag (check out BF&S if you want to read about them all) but only these come up regularly:

• subfield a contains the ISSN, with a hyphen between the 4th and 5th digits (0044-0191)
• subfield 2, when it is present, contains a code that tells you who assigned the ISSN  
• 0    ISSN International Centre
• 1     United States 
• 2     United Kingdom 
• 4     Canada 
• z     Other

The 022 tag defines the first indicator as "international interest" and this tells you whether a full record for the number is maintained by the International ISSN Centre (value=0) or not (value=1). This indicator is often blank, however, which means "not specified."