An ISIL identifies an organization, i.e., a library or a related organization, or one of its subordinate units, which is responsible for an action or service in a bibliographic environment (e.g. creation of machine-readable information). It can be used to identify the originator or holder of a resource (e.g. library material).

The ISIL is intended for use by libraries and agencies doing business with libraries, such as suppliers and publishers.
An ISIL identifies an organization, or one of its subordinate units, throughout its life.
In some cases, such as when an organization has moved or undergone a significant administrative change (e.g. a merger with another organization), particularly one that results in a name change, more than one ISIL identifier may be assigned.
Since the standard allows use of existing codes to be incorporated into the ISIL, it is possible that a given organization may have more than one ISIL, however, the intent of the standard is to minimize the number of codes.

Any library or related organization, library administrative unit or subordinate unit, acting autonomously, which is engaging in international library or booktrade communication, may be assigned an ISIL.

An ISIL is not intended to be used to classify organizations or their services and holdings.