OpenAIRE provides guidelines for data sources to promote interoperability and support open access mandates. The guidelines have expanded over time to include additional types of data sources and non-textual content. Guidelines are provided for literature repositories, data repositories, and CRIS systems. The guidelines define metadata formats, elements, and encoding schemes to ensure semantic and syntactic interoperability across different types of data sources. Adoption of the guidelines by other networks like LA Referencia and RIOXX helps ensure future compatibility and support of open access policies.