The agricultural input industry has become more concentrated in the wake of recently announced corporate mergers in the sector. This article examines the environmental implications of corporate concentration in the agricultural input sector and outlines the challenges of establishing effective international policy and governance on this issue. The article makes two arguments. First, corporate concentration matters for food system sustainability. Consolidation in the global seed and agro-chemical industries has been deeply entwined with the rise of industrial agriculture, which has been associated with a host of environmental problems including an increase in agro-chemical use and the loss of agricultural biodiversity. Second, although corporate concentration has important sustainability implications, there is little recognition of the potential connection between these issues in international governance measures. The article outlines a number of factors that discourage the development of policy and governance on these issues, including the lack of a clear scientific consensus on how best to promote sustainable agriculture; the weak and fragmented nature of regulatory frameworks and institutions that oversee competition policy and food system sustainability; the power of agribusiness firms to influence policy outcomes; and the complex and distanced nature of the underlying drivers of corporate concentration in the sector.