"Interoperability Levels for Dublin Core Metadata", published today as a DCMI Working Draft, discusses the 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. At Level 3, data is structured as Description Sets (i.e., as records). At Level 4, data content is subject to a shared set of constraints (as described in a Description Set Profile). Conformance tests and examples are provided for each level. The Working Draft represents work in progress for which the authors seek feedback. Interested members of the public are invited to post comments by 1 December 2008 to the DC-ARCHITECTURE mailing list, including "[Public Comment]" in the subject line.