Fields within the block 4XX are used to show the relationship between the continuing resource being recorded and related or otherwise connected continuing resources. Fields 41X and 42X specify the hierarchical relationship of parts to the whole work (subseries, supplements), fields 43X and 44X specify the chronological relationship (preceding or subsequent titles), and fields 45X and 488 specify the horizontal relationship (different editions, editions in other languages and scripts or otherwise connected publications).

In the records for continuing resources, fields from 4XX block may contain subfields a – Title proper/Key title and x – ISSN. A title proper and an ISSN of related continuing resource are entered in these subfields. If there is already a record in the shared COBIB database for the related continuing resource from field 4XX containing data on key title, a subfield a may not be entered.

In fields from 4XX block only the indicator 2 is defined, indicating a note display. If the indicator 2 is set to "1" – Make a note, a note is to be generated containing corresponding introductory phrases, a title and an ISSN if it is available.

In records for monographs there are fields within the block 4XX that are to be embedded. In fields 421, 423, 481, 482 and 488 fields are embedded with subfield 1. In subfield 1 the field designation of chosen field is entered together with belonging indicators. It is succeeded by subfields now prepared for data entry.