From a design science perspective, information systems and their components are viewed as artefacts. However, not much has been written yet on the ontological status of artefacts or their structure. After March & Smith’s (1995) initial classification of artefacts in terms of models, constructs, procedures and instantiations, there have been only a few attempts to come up with a more systematic approach. After reviewing previous work, this conceptual paper introduces an ontology of IS artefacts. It starts with an ontological characterization of artefacts and technical objects in general and proceeds to introduce a systematic classification of IS artefacts and compare it with existing work. We end with some practical implications for design research.