Food systems are highly complex and are driven by many economic, social, cultural, and environmental factors. In order to meet global challenges in the coming decades, a better knowledge of food system dynamics is essential to better understand how to strengthen food and nutrition security outcomes simultaneously and improve the social, environmental, and economic performance of food systems. There is a constant call for enhanced metrics to design and implement policies that address the nexus of agriculture, food, health, and the environment. Policymakers, researchers, and local practitioners are thus striving towards the identification and development of indicators in support of sustainable food systems. This chapter reports on a joint project led by Bioversity International and the International Center for Advanced Mediterranean Agronomic Studies-Mediterranean Agronomic Institute of Montpellier (CIHEAM-IAMM) to build consensus among the multidisciplinary food research community around a set of indicators (specific to the Mediterranean context) that can assess the different dimensions of the sustainability of food systems with the view to inform policymakers. Applying a Delphi survey, consensus was finally reached after three rounds of consultations involving 52 experts for 14 indicators. The application of the Delphi method in the study provides several lessons to enhance validity, replicability, participation, and consensus for further Delphi surveys.