Software Engineering Environments (SEEs) are systems designed to support software development and maintenance, and also for supporting project control and management. They provide means to integrate developers with the software process and the supporting technology. Since during software development many information resources are produced and used, it is very important to add semantics to them in order to improve the assistance given by the environment. In this context, ontologies are a key enabling technology for Semantic SEEs (SSEEs). A SSEE can be viewed as a SEE in which part of the information handled has associated a formal meaning (semantics), augmenting its tools’ ability to work in conjunction with each other and with human developers. This paper discusses how ontologies are used in ODE, an Ontology-based software Development Environment, to make it a SSEE.