Participatory Plant Breeding (PPB) is one of the areas of Participatory Technology Development (PTD) in which collaboration of researchers and farmers has been reported as quite successful although its institutionalization remains problematic. This paper aims to contribute to better understanding of PPB processes. It focuses on the practices of developing a common bean variety (Phaseolus vulgaris L.) by a group consisting of a breeder, farmers and NGO technician in northern Nicaragua. The description is an example of a technography and uses the concept of boundary object to analyse how actors come together around a shared goal and how their knowledge and practices are combined in the material making of five varieties, eventually leading to JM-12.7 as a formally released variety. The material making of five bean varieties is central in the first part of the process and shows how in practice different knowledges within the group interact. The second part of the process leads to distinguishing socio-political boundaries. The formal registration of JM-12.7 required crossing of these boundaries and prompted the reorganization of the group into a co-operative.