The paper presents an ontology-based approach to service discovery, apt to support flexible and efficient matchmaking between service descriptions. We propose a hybrid approach that combines two matching strategies: a deductive strategy based on Description Logics with a reasoning procedure exploiting ontology knowledge to assess the type of match among services; a similarity-based strategy exploiting information retrieval metrics to measure the degree of match among services. Keywords Semantic Web Services, Ontology-based Service discovery, Service Ontologies, Hybrid Matchmaking