Emergency management becomes more challenging in an international crisis episode because of cultural, linguistic and legal differences between all stakeholders, especially first responders. Misunderstandings between first responders makes decision-making slower and more difficult. However, spread and development of networks and Emergency Management Systems (EMS) has improved emergency responses, becoming more coordinated. Despite improvements made in recent years, EMS have not still solved problems related to cultural, legal and linguistic differences which are the real cause of slower decision-making. In addition, from a technical perspective, the consolidation of current EMS and the limitations of their exchanged data formats offers another problem to be solved in any solution proposed for information interoperability between heterogeneous EMS surrounded by different contexts.To overcome this problem, a two step solution is proposed: (i) As main objective and foundations of this proposal, the development of a common and modular ontology shared by all the stakeholders offers the best solution to gather all stakeholders knowledge in a unique and flexible data model, taking into account different countries cultural, linguistic and legal issues (ii) Taking advantage of the fact that most legacy Emergency Management Systems are based on Service-Oriented-Architectures (SOA), i.e. they collect information from services offered by other systems (e.g. Geographic Information Systems), the interoperability burden will be addressed by means of transparent SOA mediation algorithms compliant with current data formats and existing solutions.Taking into account the heterogeneity and diversity of all existing scenarios in crisis episodes, the potential results of this proposed ontology-based interoperability solution will be validated through the design and development of a realistic prototype scenario actively involving both emergency managers and emergency first responders.