Modern ruminant production systems have to meet the sustainability challenge. Achieving this aim will require changes in all part of the production systems, including feeding. Today, diet formulation for ruminants has to supply a diet balanced in all nutrients and free from harmful substances, to meet production objectives and thereby generate, using ecological practices, animal products that are safe for humans. This requirement implies extending the ruminant diet evaluation concept to cover new dimensions other than feed value, such as impact on animal health, emitted wastes and the quality of ruminant products. Here, we present the concepts of a multi-criteria evaluation of ruminant diets, and the method we used to define the criteria and their indicators. Twenty-four criteria adapted to dairy ruminants and ranked in four categories of impact (animal production and health, wastes emitted and quality of the animal products) are proposed. Then, we discussed the type of indicators required to assess these criteria and identified the works to be carried out on indicators development. Finally, we discuss the steps remaining for the construction of the multi-objective diet evaluation tool.