This thesis explores initiatives in 'biofortification', a term referring to the enhancement of micronutrient levels of staple crops through biological processes, such as plant breeding and transgenics. It traces developments in i'ice bioforiification; fromtwo early initiatives. in iron rice research and 'Golden Rice', to the HarvestPlus 'Challenge Programme', launched by the CGIAR in 2003, with substantial support from the Gates Foundation. It highlights a series of transformations that have punctuated the journey of biof0l1ification research, from its modest beginnings at the outer margins of international crop research, to its re-branding as an exemplar of a new way forward identified for the CGIAR, as 'broker' in heterogeneous, global research networks,_ a.ble to guarantee the 'public goods' status of the _agendas and outputs of such networks. International biof0l1ification initiatives such as HarvestPlus emphasise three, inter-related themes: managing research collaboration through multi-organisational partnerships; tackling complex problems through i11lerdisciplinwy research; and achieving greater impact, as understood within the MDG framework that now dominates international development thinking. This research asks if these evolving modes of organisation, styles of science and framings of impact are indicative of future directions in international agricultural research. These questions have been followed through a multi-sited, ethnographic tracing of science policy processes and institutionalised practices, from the United States to the Philippines and China. Biofortification provides a lens through which to question the idea of 'global science', and the notion, built into the fabric of the CGIAR system, that it can generate generic research outputs as widely applicable, international public goods. This is particularly relevant at a time when donor attention has returned to agriculture, and to the potential of investments in science and technology to stimulate agricultural development. In practice, as biofortification research has become increasingly 'global', attention has shifted upstream, relocating the locus of decision making ever further from the beneficiary groups in whose name such substantial investments are made. These dynamics implicitly sanction a return to top down development; while restricting the space for actors located fUl1her downstream to debate unresolved technical and policy uncertainties.