Abstract: This paper describes the work that is being done within the EU research project DISASTER to solve interoperability issues in cross-border emergency operations by applying a technical solution that is able to create a common operational picture. To that end a twofold solution is proposed: The development of a common and modular ontology shared by all the stakeholders taking into account different countries cultural, linguistic and legal issues. And, from that point, bearing in mind that most legacy EMSs (Emergency Management Systems) rely on Service-Oriented-Architectures (SOA), the implementation of transparent SOA mediation algorithms compliant with current data formats and existing solutions. That way, a mediation solution is provided by the DISASTER Mediator, which plays the role of gateway for each EMS enabling a communication based in Web Services. In order to avoid a misunderstanding of shared information it is necessary to create a solution that offers more than a plain translation of terms but rather a concept mediation so the corresponding user is able to understand the situation in its own framework of reference.