This paper is to investigate some general features of social tagging and folksonomies along with their advantages and disadvantages, and to present an overview of a tag ontology that can be used to represent tagging data at a semantic level using Semantic Web technologies. Several tag ontologies have been developed with a specific purpose and used in various websites. However, in order to represent tagging data at semantic level existing tag ontologies need to be interlinked, since individual tag ontology cannot represent overall features of tagging activities. After introducing conceptual overview of tagging and folksonomies and tag ontologies, we will propose the combinational model for linking tag ontologies.