An ISIL consists of a prefix identifying the authority which issued the ISIL, a dash, and then an identifier issued by that authority. All two letter prefixes are reserved for the ISO 3166-1 alpha-2 country code, followed by an identifier assigned by that country's national library authority. Global-level identifiers can also be assigned, which are not associated with a particular country, e.g. 'oclc-' for the OCLC. The suffix is generally a pre-existing system of identifying libraries; thus, ISIL unifies existing systems around the world rather than instituting an entire system from scratch.
- "ISO 15511:2011 - Information and documentation -- International standard identifier for libraries and related organizations (ISIL)". ISO. 2011-08-22. Retrieved 14 June 2014.
- "ISIL Registration Authority". Danish Agency for Culture and Palaces. Retrieved 3 February 2021.