The measure is a game changing solution presented to the UN Food System Summit 2021 calling for a fundamental re-think of how seed system development is supported globally. Our proposal is to ensure and promote – through legislation, seed policies and action – that farmers have access to a diversity of well adapted varieties of crops that meet agroecological, nutritional and cultural needs and preferences. Farmers’ seed systems are key to provide farmers with access to both local varieties developed over millennia of farmer selection and varieties developed with modern plant breeding. We call for a bottom-up demand-driven approach to seed security to complement the currently dominant top-down supply-side approach, thereby supporting farmers’ agency and recognizing farmers’ seed systems contribution to global food security.