This online publication provides access to both the full and concise versions of the MARC 21 Format for Holdings Data. The "full" holdings format contains detailed descriptions of every data element, along with examples, input conventions, and history sections. The "concise" holdings format contains abridged descriptions of every data element, along with examples. The full and concise versions are identified in the header of each field description.

Changes to the MARC 21 Format for Holdings Data that resulted from Update No. 25 (December 2017) are displayed in red print. The date located in the header of the full version of each field indicates the last month and year of update.