International public agricultural research for development is increasingly requested to contribute to solving societal challenges related to food security, ecological transitions, climatic change and inequalities in development, among others. At the same time, in one strand of the scientific communities modalities and criteria to assess research are shifting towards demonstrating and explaining the causal link between research outputs and development impacts (Gaunand et al;, 2015). This paper describes a novel approach for impact assessment of agricultural research conducted in a developing country context adapted from the “impact pathways” and ASIRPA approaches (e.g. Douthwaite and Gummert 2010; Joly et al., 2015). A key methodological choice was to give an active role in the assessment to the multiple stakeholders involved in innovation and/or impacted by it. This was considered essential to identify impacts and indicators that evaluation teams might not have thought of by themselves, and to understand the complexity of innovation processes eventually leading to impact, particularly in a developing country context for which accountability towards end-users of research is weak and availability of or access to reliable quantitative data is a challenge. The resulting participatory methodology, called “Impress” (IMPact of RESearch in the South) focuses on establishing and explaining the relationships between the outputs produced by research, the outcomes that involve and affect the actors directly or indirectly interacting with research and ultimately the primary and secondary impacts for development. After developing it iteratively over several years, CIRAD is currently testing it by assessing 13 case studies throughout Africa, Asia and Latin America. Cases cover a wide diversity of innovation domains (plant breeding, post-harvest processing, pest and disease management, value chains, etc.), research approaches (from transfer of technology to action-research) and inn