In this chapter, we describe an infrastructure enabling archetype-based semantic interoperability of Web service messages exchanged in the health care domain. We annotate the Web service messages with the OWL representation of the archetypes. Then, by providing the ontology mapping between the archetypes, we show that the interoperability of the Web service message instances can be achieved automatically. An OWL mapping tool, called OWLmt, has been developed for this purpose. OWLmt uses OWL-QL engine, which enables the mapping tool to reason over the source archetype instances while generating the target archetype instances according to the mapping patterns defined through a GUI.