Recently, the methodology of design experiments has received some attention in the literature, with special issues devoted to it in Educational Researcher (2003) and Journal of the Learning Sciences (2004). Much more work is needed to clarify the role of context and of theory in design research, and to demarcate design research from other methodologies such as case studies, ethnography, and scientific experiments. The emergent (non-linear) character of design experiments on knowledge building, as practiced in this community in the last decade, is not adequately represented by the literature. In other words, the view represented by the literature is too rational. The goal of this session is to articulate clearly how we understand design experiments and their value to the creation and mobilization of knowledge.