| 01 | Proprietary | Note that <IDTypeName> is required with proprietary identifiers | 11 | |
| 02 | Proprietary | Deprecated – use code 01 | 1 | 11 |
| 04 | Börsenverein Verkehrsnummer | | 1 | |
| 05 | German ISBN Agency publisher identifier | | 2 | |
| 06 | GLN | GS1 global location number (formerly EAN location number) | 1 | 9 |
| 07 | SAN | Book trade Standard Address Number – US, UK etc | 1 | |
| 12 | Distributeurscode Boekenbank | Flemish supplier code | 7 | |
| 13 | Fondscode Boekenbank | Flemish publisher code | 7 | |
| 16 | ISNI | International Standard Name Identifier (used here to identify an organization). Only for use in ONIX 3.0 or later. See https://isni.org/ | 57 | |
| 23 | VAT Identity Number | Identifier for a business organization for VAT purposes, eg within the EU’s VIES system. See http://ec.europa.eu/taxation_customs/vies/faqvies.do for EU VAT ID formats, which vary from country to country. Generally these consist of a two-letter country code followed by the 8–12 digits of the national VAT ID. Some countries include one or two letters within their VAT ID. See http://en.wikipedia.org/wiki/VAT_identification_number for non-EU countries that maintain similar identifiers. Spaces, dashes etc should be omitted | 16 | |