In the field of ubiquitous computing, a class of applications called context-aware services attracted great interest especially since the emergence of wireless technologies and mobile devices. Context-aware application can dynamically capture a range of information from its environment and this information represents a context, the application adapts its execution according to this context. An important challenge in ubiquitous computing is dealing with context. Ontologies presents the most promising instrument for context modeling and managing due to their high and formal expressiveness and the possibilities for applying ontology reasoning techniques. In this paper, we present an ontology based approach for the development of context aware services.