With the advancements of semantic web, ontology has become the crucial mechanism for representing concepts in various domains. For research and dispersal of customized healthcare services, a major challenge is to efficiently retrieve and analyze individual patient data from a large volume of heterogeneous data over a long time span. This requirement demands effective ontology-based information retrieval approaches for clinical information systems so that the pertinent information can be mined from large amount of distributed data. This unique and groundbreaking book highlights the key advances in ontology-based information retrieval techniques being applied in the healthcare domain and covers the following areas: Semantic data integration in e-health care systemsKeyword-based medical information retrievalOntology-based query retrieval support for e-health implementationOntologies as a database management system technology for medical information retrievalInformation integration using contextual knowledge and ontology mergingCollaborative ontology-based information indexing and retrieval in health informaticsAn ontology-based text mining framework for vulnerability assessment in health and social careAn ontology-based multi-agent system for matchmaking patient healthcare monitoringA multi-agent system for querying heterogeneous data sources with ontologies for reducing cost of customized healthcare systemsA methodology for ontology based multi agent systems developmentOntology based systems for clinical systems: validity, ethics and regulation