Human factors/ergonomics (HFE) as a discipline has grown by accretions rather than having been developed systematically and deliberately. The goal of this work is to create a formal conceptual structure for HFE. A disciplinary history is highly specialized, but the author maintains that HFE is distinctive in being the only discipline that relates humans to technology. Other behavioural disciplines like anthropology have little connection with technology, and this is what makes HFE important in the present historical era.