This contribution aims to understand the specificity of thinking and making social innovation, within and through the design field and its practice. The first part of this paper frames the relationships between project and design, characterising their definitions and goals. Design is presented as a discipline and field of action, where both thinking and the project process are directed at reaching a sustainable change in society. The second part of the paper presents how social innovation by design leads to new epistemological questions and dimensions within design's practices and challenges. Consequently, the University of Nimes' pedagogical and research-­‐driven design initiative illustrates how a commitment to social innovation by design has fostered new productive practices and knowledge, in turn leading to new forms of participation, collaboration and interaction between actors and users. In our experience, mixed methods and interdisciplinary dialogues are key elements in achieving social innovation by design.