Resolve one or more editions by identifier: ISBN-10, ISBN-13, OCLC, LCCN, or Open Library Edition ID (OL…M). Every identifier in a call shares one id_type — pass id_type "isbn" for both ISBN-10 and ISBN-13. Up to 50 identifiers resolve in a single upstream request, so a bibliography or shelf export costs one call rather than one per book; a large batch is a large response, so ask for what you need. Returns full edition metadata including authors, publisher, language, all identifier types, and the parent work ID, with author names inline and no secondary lookup; when the edition record itself lists no authors, they are recovered from the parent work and marked as such, and a notice names any edition whose recovery failed. Partial success is the norm — identifiers that resolve come back in editions, the rest are listed in unresolved with a reason, and the call fails only when nothing resolved.