Seaweed has been receiving increasing attention as a novel food source worldwide. To optimally develop seaweed's food provisioning potential, the seaweed value chain requires further understanding. To this end, we used the Food System Approach to review the existing knowledge on seaweed as food source. We identified opportunities, constraints and knowledge needs relevant to fulfilling the potential of seaweed to contribute to food security. Thereby, we especially focus on optimizing and upscaling seaweed production and environmental sustainability. Our review shows that although progress has been made in solving technological issues in seaweed production, major knowledge gaps regarding social and economic factors remain. More attention to these issues can help realize the food potential of seaweed.