This article contributes to methodological studies of constructive design research by explicating its underlying epistemological foundations. At the heart of this article is the notion of drifting, defined as those actions that move design from its original objective or question to sometimes unanticipated results. The article explicates four traditions of knowledge production as derived from a corpus based on PhD theses. These traditions relate knowledge production to methods, research programs, design experience, and to a dialectic between researchers and user communities. As a result, they form epistemological traditions.