This current research builds on earlier analytic projects on engineering design methods and on the concepts of technical artefact and technical function. These projects originated in the Dual Nature of Technical Artefacts research programme at Delft University of Technology. Starting point of this programme was that technical artefacts have both a structural and an intentional nature, because a complete description of a technical artefact refers to the physical make-up of the artefact and to the goals the artefact is to realise. Engineering design was taken as an activity that relates these natures, since it has goals of artefacts as input and the physical description of these artefacts as output. And technical function was taken as a bridging concept, since a function of an artefact highlights a physical capacity of the artefact by which users can realise the goals associated to the artefact. My Dual Nature research, regularly done together with Wybo Houkes (Eindhoven University of Technology), resulted in an action-theoretical analysis of the design and use of artefacts, in a philosophical account of technical functions, called the ICE-theory, and in a text book on philosophy of technology.