Abstract. As the Semantic Web emerges the problem of semantic heterogeneity is becoming more acute. Ontology matching techniques aim at tackling this problem by establishing correspondences between elements of the ontologies. These techniques rely on distance metrics, often called (dis)similarity measures, to assess the similarity of elements within the ontologies. Most of these approaches are either terminological, structural and/or extensional. However, recently some proposals for semantics-based measures have been put forward. We reason that these latter should receive more attention, since semantics are one of the key advantages of ontologies. Therefore, we present a set of semantic ontology similarity measures.