Indices are composite tools aiming to measure and quantify a variety of clinical conditions, behaviors, attitudes and beliefs that are difficult to be measured quantitatively and accurately. In this review, the methodology used to develop dietary indices and their relationship with health determinants and outcomes is discussed. In brief, the already proposed indices are adequate tools concerning the evaluation of diet quality, but they have shown moderate predictive ability in relation to chronic diseases and health determinants. The aforementioned weaknesses could be attributed to: inappropriate selection of the components (i.e., number or content of dietary information), selection of small number of cut-off points for each component and/or equal contribution of all index items to the calculation of the total score. Nevertheless, dietary indices are important tools to evaluate not only the diet quality, but also the relationship between dietary habits and several health outcomes.