Component-based software engineering on the Web differs from traditional component and software engineering. We investigate Web component engineering activites that are crucial for the development,com position, and deployment of components on the Web. The current Web Services and Semantic Web initiatives strongly influence our work. Focussing on Web component composition we develop description and reasoning techniques that support a component developer in the composition activities,fo cussing here on matching. We show how a component model can be integrated into a Semantic Web-style ontology for component development.