National Bibliography Number (NBN) is a group of publication identifier systems used by national libraries in countries such as Germany, Italy, Finland, Norway, The Netherlands and Sweden. There is no global standard for the contents of NBNs; instead, they have a country-specific format. NBNs are typically used for documents which do not have a publisher-assigned identifier such as an ISBN. They can be used to identify persistently media that are archived in national libraries, for instance Ph.D. theses.

A Uniform Resource Name (URN) namespace for NBNs has been assigned [1], and is described in IETF RFC 3188 RFC 8458. For example:

An NBN in Germany (de), in Bavaria (bvb = Bibliotheksverbund Bayern), library number 19 (University Library Munich), pointing to a PhD thesis on heat detection in cattle.

Some libraries, such as the National Library of Sweden, provide a resolution service for these URNs.[2]

In Italy an NBN (NBN:IT) is assigned to digital resources deposited in the National Legal Deposit service [3]. The NBN:IT resolver is active at: http://nbn.depositolegale.it/

In The Netherlands the NBN (URN:NBN:NL) is assigned by the National Library (KB)