"Interoperability Levels for Dublin Core Metadata" has been published as a Recommended Resource. The document discusses modeling choices involved in designing metadata applications for different types of interoperability. At Level 1, applications use data components with shared natural-language definitions. At Level 2, data is based on the formal-semantic model of the W3C Resource Description Framework (as in Linked Data). At Levels 3 and 4, data also shares syntactic constraints based on the DCMI Abstract Model. The document aims at providing a point of reference for evaluating interoperability among a variety of metadata implementations. The authors expect this document to evolve as the trade-offs and benefits of interoperability at different levels are explored and welcome feedback from its readers.