As key economic, ecological and demographic trends converge to reshape Africa and its relationship with the outside world, a new politics is emerging in the twenty-first century around the water–food–energy nexus, which is central to the continent's relevance in the global economy. On the one hand, Malthusian anxieties are proliferating; pessimists link population growth and growing water scarcity to state failure and ‘water wars’. On the other hand, entrepreneurs, sovereign wealth funds and speculators consider Africa's potential in water resources, energy production and food output as one of the last great untapped opportunities for the global economy: Africa is on the brink of an agro-industrial transformation. This article examines how African actors are not merely responding to economic and environmental changes but also thinking politically about water, food and energy security. Many of them are seizing the new opportunities to redefine their national politics, their relationship with local communities and their ties with external players, regionally and globally. Ethiopia's project of hydro-agricultural state-building helps to identify the most important fault lines of this new politics at the national, local and international level. The politics of water security and energy development simultaneously puts African states and their populations on the defensive, as they grapple with huge challenges, but also provides them with unique opportunities to take advantage of a more favourable global configuration of forces.