In order to enable teachers to share and reuse learning objects these objects should be described using standard metadata such as the IEEE?s Learning Object Metadata. Learning object metadata elements must be described using appropriate vocabularies in order to ensure semantic interoperability and facilitate resource description discovery and reuse. LOM elements can be described using simple vocabularies and value lists, LOM vocabularies, taxonomies, classifications and thesauri and natural language. CEN/ISSS has funded the development of a registry of taxonomies and vocabularies relevant for a European learning society. It is recommended that metadata implementers publish their vocabularies in the registry to reduce duplication of effort and facilitate semantic interoperability.