In On Knowledge, leading design thinker Clive Dilnot poses the questions: What does design know? What is the nature of design knowledge? This short book brings together three key writings by Dilnot on the relation of design and understanding. Design as Socially Significant Activity reads design in its social context, and links ethical issues with questions of design understanding and design knowledge. In The Science of Uncertainty, Dilnot examines the general lack of knowledge concerning the invisibility of design as knowledge. Linked also to the onset of the 'artificial', Dilnot sets out an agenda for understanding design as a mode of knowing essential to deciding how we should act in the emerging world. Finally, Design, Knowledge and Human Interests considers the complex and important relations of theory and practice in knowing. This is an important update of one of Dilnot's seminal theoretical works, and it should be of interest to all design scholars and practitioners.