Knowledge plays a vital role in our life in that it reflects how we understand the world around us and thus determines how we act upon it. In this sense, knowledge is of particular importance for designers because they act to shape our world. Conventionally, knowledge creation has been assumed by (design) research. However developments of using practice within research have pointed to knowledge creation within and through practice. This has raised the question of the meaning, role and format of knowledge in both research and practice, and about the compatibility between knowledge of research and practice. The research presented in this paper has set out to investigate the concept of knowledge with regard to this question. The paper begins by considering some of the main problems with knowledge in research within design, and more generally in the creative and practice-led disciplines. It then examines the meaning of knowledge in relation to its philosophical foundations. On this basis, the discussion reconsiders the meaning, role and format of knowledge, and the impact of this for the conduct of research.