Although it is not yet known for certain what will replace MARC, eventually bibliographic data will need to be transformed to move into a linked data environment. This article discusses why the National Library of Medicine chose to add Uniform Resource Identifiers for Medical Subject Headings as our starting point and details the process by which they were added to the MeSH MARC authority records, the legacy bibliographic records, and the records for newly cataloged items. The article outlines the various enhancement methods available, decisions made, and the rationale for the selected method.