This chapter analyses the classical tripartite model and establishes work in agrifood systems. It suggests replacing social, economic, and environmental sustainability with three new legs calling for research and action based on agroecology, food sovereignty, and food justice. The chapter offers a new conceptualization of sustainability in order to remedy some of the deficiencies of the traditional model as it applies to food security and the sustainability of food and farming systems. It refines definitions of sustainability beyond the agrifood context. Food sovereignty prioritises local and national economies and markets and empowers peasant and family farmer-driven agriculture, artisanal fishing, pastoralist-led grazing, and food production, distribution and consumption based on environmental, social and economic sustainability. Food justice addresses how stark conditions of racial, gendered and class-based urban inequality produce significant barriers to accessing affordable and healthy food for many inner city residents.