Using metadata for referencing multimedia material is becoming more and more usual. This allows better ways of discovering and locating this material published on the Internet. Several initiatives for establishing standards for metadata models are being carried out at the moment, but everyone focuses on their own requirements when defining metadata attributes, their possible values and the relation between them. From the point of view of someone who wants to seek and buy information (multimedia content in general) in different environments, this is a real problem, because he has to face different metadata sets, and so, must have different tools in order to deal with them. In this paper, we present a model for the interoperability of different metadata communities, where neither the publishers nor the customers have to be aware that they all may be working with different metadata models. We are mapping the semantics of different metadata models with the objective of not loosing information when the user and the content provider use different metadata schemas. A "metadata agent" is used to carry out the interoperability information.