We examine the transnational governance of biofuel sustainability and its coexistence with the WTO trade regime. The way in which the EU Renewable Energy Directive (RED) is shaping transnational biofuel governance shows deep and mutual dependence between public and private. The EU relies on a private system of compliance and verification, but private certification schemes are dependent on the incentives provided by RED to expand commercially. A second layer of hybridity in this governance system is that it is emerging in the shadow of the WTO. EU policymakers refrained from introducing binding requirements for social sustainability criteria in RED, and left private certifiers to fill this gap. Our discussion also serves to introduce the symposium on the ‘Transnational Hybrid Governance’ (THG) of biofuels. The three contributions to the symposium analyse the complex making and mutual shaping of biofuel sustainability and discuss the institutional features, processes, networks, and sociotechnical devices by which markets are organised, and economic and political orders take shape.