ISSN is an identifier for continuing media

An ISSN or International Standard Serial Number is an 8-digit code used to identify newspapers, journals, magazines and periodicals of all kinds and on all media. It is associated with the title of the publication (eg journal name).

The format is 8 digits or 7 digits and an X, in 2 groups of 4, where the last digit is a check digit.

There may be 2 ISSNs assigned to the same resource if it is published in both print and electronic formats. The print one is usually the default, and may be called p-ISSN. This may also be used as the “linking ISSN” or ISSN-L, to relate instances of the same work together. The electronic one may be called e-ISSN or EISSN.

You can search by ISSN on worldcat like worldcat.org/ISSN/1234-4567 and it will resolve to a record by searching worldcat’s registers, not the international ISSN Register.