Eric, WorldCat Metadata API provides read and write API access to the data in WorldCat: bibliographic records, local bibliographic data and basic holdings. WorldCat Discovery API provides access to search WorldCat and OCLC's Central Index of metadata based on a diverse set of indexes. Data is returned in a Linked Data graph. This API is still in beta. For more detailed information on each API you can look at the documentation at WorldCat Metadata API - http://www.oclc.org/developer/develop/web-services/worldcat-metadata-api.en.html WorldCat Discovery API - https://www.oclc.org/developer/develop/web-services/worldcat-discovery-api.en.html Given the use case you describe, your best bet is probably the WorldCat Metadata API, especially if you need to write any data back to WorldCat. However you can perform the same task with WorldCat Search API and if you are only reading data this might be a better fit because of its simpler authentication method. You're welcome to send an email to [log in to unmask] if you have further detailed support questions. Karen On Tue, Mar 22, 2016 at 6:15 AM, Eric Lease Morgan <[log in to unmask]> wrote: > I’m curious. What is the difference between the WorldCat Discovery and > WorldCat Metadata APIs? > > Given an OCLC number, I want to programmatically search WorldCat and get > in return a full bibliographic record compete with authoritative subject > headings and names. Which API should I be using? > > — > Eric Morgan >