Since March 1998, the U.S. Government Printing Office has used persistent uniform resource locators (PURLs) to provide libraries and other parties stable URLs to online Federal information. If a user clicks on a PURL found on a library Web page or in a library catalog, the request will be routed to the Federal publication. Libraries do not need to update the PURLs in their catalog records or Web pages since GPO staff will modify PURL entries as the location of the Federal information changes and GPO’s PURL server will route traffic to the appropriate Web site.

GPO performs routine maintenance on PURLs and their bibliographic records. Broken PURLs can be reported using askGPO. If the Federal agency host removes the content from their Web pages altogether, GPO will modify the PURL to route online traffic to a copy on its own data repository if it has been "harvested" or archived. This will ensure that when a user visits the PURL it is always up-to-date with the most current information. If GPO cannot obtain an online version of the Federal information, the PURL record will be modified to link to a page that states that as of a certain date that the information was no longer available online.