The web service associates library catalog records from WorldCat with related resources based on ISBN. Submitting an ISBN retrieves a list of ISBNs for records related by an algorithm from OCLC, the primary organization managing professionally cataloged bibliographic records, along with selected metadata from those records. The linkages support "FRBRized" grouping of related editions, such as other expressions of the same work and manifestations of the same expression.
API methods get records and/or metadata for resources related to the one whose ISBN is submitted. Methods also support mapping of other books-related identifiers, such as xOCLCNUM and convert between 10- and 130-digit ISBNs.