ART Inv. (i.e. "inventory") numbers are temporary call numbers that act as pseudo-accession numbers for uncataloged material that cannot be given a six-digit accession number while awaiting cataloging.

ART Inv. numbers 1 through 453 were assigned to uncataloged art in the early 1950s. Most of these have since been given ART File, Box or Vol. call numbers. Approximately 55 still have their ART Inv. call numbers.

In October 2002, ART Inv. numbering resumed in order to assign unique identifiers to the approximately 300 non-book and non-manuscript items that had no call number or accession number, but had long been part of the collection (often from Mr. and Mrs. Folger's time).

Numbering resumed at ART Inv. 1001 rather than 454 in order to keep an easy count of how many numbers are assigned in the new round of numbering. The items are shelved in numeric order within their material groupings, with the default location being the flat shelves following ART Inv. 1 through ART Inv. 453. Other material receive call number suffixes as is done with new accessions, e.g. "(framed)" for hanging pictures and "(realia)" for objects, along with a more specific location.