In this section, we discuss the notion of ontology in relation to the Scottish Building Regulations. There is no formal ontology associated with these regulations, and the interest here is partly in investigating why. This is therefore less a case-study than the study of a non-case, but we hope that it will point to some useful issues about the potential role of ontologies in cases like this, and in related contexts. The fact that the regulations are part of a legal framework seems to be important, and highlights issues about when and why it is considered important for definitions to exist and be clear, and the importance of attention to the needs and practices of the communities using the terminology. Questions that arise include which terms are defined, how terms are used that are not defined, and how in practice concepts are used and worked with.