Skills management has been recently acknowledged as one of the key factors to adequately face the increasing competitiveness between knowledge intensive companies. In this paper we present a formal approach to Ontology-Based Semantic Matchmaking between Skills demand and supply, devised as a virtual marketplace of knowledge. In such a knowledge market metaphor, skills are a peculiar kind of good that has distinguishing characteristics with respect to traditional assets. Buyers are entities that need the skills of people, such as projects, departments and organizations, sellers are workers that offer their own skills. The formal framework supports the semantic match of descriptions provided by demanders and sellers of skills. In particular...