Legumes are essential to agrifood sustainability transition. Their nutritional values contribute towards healthy diets, a reduction in animal-based protein consumption and in nitrogen fertilization in crop rotations, therefore meaning a reduction in agricultural greenhouse gas emissions. However, legume consumption remains low in Europe, and institutional food services (IFS) could be an important lever for fostering new eating habits. This study aims to investigate legume use in IFS and identify brakes and levers in their promotion. We built a socio-technical framework to analyse: frequency and diversity of legumes served; cooking practices and uses of legumes in dishes, including alternative (vegetarian/vegan) dishes; and legume-sourcing strategies through supply chain organisations and eco-labels. We addressed a wide survey to IFS kitchens in France, the largest IFS sector in Europe. Based on 383 complete answers, we have revealed heterogeneous IFS practices through clustering methods. This first and original study demonstrates how even if they are few in number (16%), kitchens that develop legumes the most are also those with the strongest sustainability profile (more alternative dishes, local and organic sourcing). Moreover, our clustering analysis revealed that self-managed and medium-sized kitchens are more committed to sustainable practices regarding legumes. Legumes are least served in the Education segment. We discuss ways to foster legumes through the IFS sector, based on cooks’ training, recipes and technical infrastructures, and consumer recognition of legume benefits.