This article announces the availability of a crosswalk between ONIX 2.1 and MARC 21 developed by OCLC and illustrates how it is used in the OCLC Metadata for Publishers project. To accomplish the goal of merging library and publisher metadata and anticipating the need to mine MARC records for other purposes, the design of the crosswalk, the corresponding software, and the application take records apart and process the fields individually, creating data streams that match the intended use of the ONIX standard and resemble the pre-Internet paradigm of Electronic Data Interchange, or EDI, for describing materials and tracking them through a supply chain. Though this design works well enough to support commercial-grade processes, problems arise with mappings between physical descriptions in the two standards, which need to be more rigorously modeled or closely aligned. Nevertheless, the RDA/ONIX Framework, which is reviewed here, promises to reduce this obstacle.