Recent interest in design-based research as a research and development methodology in education has begun to clarify the goals and commitments involved in this practice. So far, we have limited views into how the work of design and the work of research impact each other in the course of design-based investigations. In this article, I use the experience of the passion curriculum project, in which I person acted as researcher and as educational practitioner to provide a close trace of the interconnections between research and design in this work. I highlight 3 key functions in design-based research: how design considerations provide a focus for developing research questions; how design moves forward on several fronts simultaneously, with some design solutions informed by research investigations and theory and others developed through engineering of locally functional solutions; and how emergent theories inform both the design of interventions and the development of lenses for investigation. Examples from the passion curriculum project expose the operation of these functions in this particular context.