An ex post analysis of the impact of research projects related to Participatory Breeding (PB) of sorghum in Burkina Faso was carried out in 2015 and 2016 using the "Impress" method developed by CIRAD. The sorghum PB approach emerged in Burkina Faso in the late 1990s as a response to the very low adoption of improved varieties released by the conventional breeding program. This approach represents a paradigm shift from a research approach focused solely on the development of "high-yielding varieties", irrespective of the social context in which these varieties are to be used, towards the development of varieties, seed and their dissemination within a multi-stakeholder framework. The present study aims to assess the impact of the sorghum PB program and the activities related to seed production and dissemination carried out in Burkina Faso over a period of 20 years. Detailed mappings of the timeline and the actors that have been involved in the innovation process, as well as the impact pathway, have been established. The causal relationships between outputs, outcomes and impacts have been developed on the basis of 67 impact descriptors provided by research partners and beneficiaries during participatory workshops. Around thirty measurable impact indicators were assessed by means of individual or focusgroup interviews and by means of secondary data sources. The three major outputs of the study were: the new improved varieties (IV) resulting from the PB actions; the mini-pack seed strategy; and the new skills acquired by the farmer organizations regarding sorghum improvement and certified seed production. The appropriation of these outputs by the farmer organizations not only brought structure to the experimentation networks, but also ensured the promotion and dissemination of the new varieties, and the establishment of a decentralised certified seed production scheme. One major positive impact was the significant increase in the use of sorghum IVs not only in the villages covered by the program but also in neighbouring areas. The expansion and performance of these new IVs has helped reduce the hunger gap while increasing the revenues of farmers involved in seed production. Furthermore, the research projects helped bring structure to the national seed sector as well as to the certified seed market, where the farmer seed production Unions consolidated by the PB projects now play an important role in the orientation of national legislation. The experimental method of impact assessment used in this analysis explores and makes visible the complex multidimensional and multi-stakeholder processes that have helped shape technological innovation and its impact on development. Such impact assessments can also elucidate the role of research in reinforcing the individual and collective capacities needed for innovating and testing out new technologies, that is, new varieties and seed production practices according to local constraints and/or opportunities.