The University of North Texas (UNT) Libraries work with a large number of identifiers in relation to our Digital Collections (The Portal to Texas History, the UNT Digital Library, and the Gateway to Oklahoma History). Since the Digital Collections comprise items from other library and campus departments, as well as a large number of cultural heritage institutions across Texas and Oklahoma, many of the materials have assigned identifiers that are important to the group that owns the physical materials. We document any relevant identifiers in each item’s metadata record, whether they belong to an international or established standard (e.g., ISSNs or call numbers) or have a specific context (e.g., agency-assigned report numbers). This presentation discusses some of the complexities inherent in managing both locally-created and externally-assigned identifiers, why we use different types of identifiers throughout our infrastructure, and the implementation of various identifiers in our Digital Collections.