Trade globalisation and climate change pose new challenges for food security in Africa. To unlock smallholder productivity, more understanding is needed of the institutional context and the role of development interventions, such as partnerships, in the food sector. This article proposes institutional logics as a theory and methodology for institutional diagnosis to gain insight into context-embedded negotiation and change processes created by project-based partnership interventions. We analyse the institutional logics of organisations active in the development of two value chains in Ghana to subsequently show how, in partnerships, these logics are negotiated in light of the objectives and interests of the intervention. The main findings are that donors, with their market and professionalisation logics, are quite influential, but many other development actors still adhere to principles of grassroots empowerment and social security. In the evolving partnership process, market logic remains strong, but coupled with institutional logics endorsing farmer empowerment and solidarity with the resource-poor. This is done in a process of bricolage in which field level implementers go against the dominant logic of project initiators: showing that newly introduced development logics are mitigated by an existing local structure fostering other development logics. The broader implication is that new development paradigms may need a considerable transition period to become mainstream. The concepts of institutional logics and bricolage as a diagnostic tool allow researchers to characterise the adherence to and blending of institutional logics by actors. This tool helps to understand the mobilisation strategy of the initiator and to follow the negotiation of logics that takes place amongst partners in partnerships. Detailed insights into the blending of potential partners' logics, pathways of negotiation processes and the plausible outcomes enable development practitioners to strategically prepare and manage their collaborative interventions.