The <journal-id> element holds an external identifier, typically assigned to a journal by a publisher, archive, or library to provide a unique identifier for the journal. The contents of this element should not be confused with the @id attribute, which holds an internal document identifier that can be used by software to perform a simple link inside the document.

There may be more than one such identifier, with the type of identifier named by the @journal-id-type attribute. For example, one identifier may be a registered DOI, another a control number assigned by the publisher, and another the journal abbreviation assigned by PubMed Central.