Ontologies are now in widespread use as a means of formalizing domain knowledge in a way that makes it accessible, shareable and reusable. Nevertheless, to many, the nature and use of ontologies are unfamiliar. This paper takes a practical approach – through the use of example – to clarifying what ontologies are and how they might be useful in an important and representative phase of the engineering design process, that of design requirement development and capture. The paper consists of two parts. In the first part ontologies and their use are discussed, and a methodology for developing ontologies is explored. In the second part, three very different types of ontology are developed in accordance with the methodology. Each of the ontologies captures a different conceptual facet of the engineering design domain, described at a quite different level of abstraction than the others. The process of developing ontologies is illustrated in a practical way and the application of these ontologies for supporting the capture of the engineering design requirement is described as a means of demonstrating the general potential of ontologies.