Nutrient density (ND) quantifies the concentration of essential nutrients in foods relative to their caloric content, serving as a cornerstone for assessing the nutrient adequacy of the foods and diet quality. The concept of ND underpins public health strategies, dietary guidelines, and food labeling initiatives to promote health and prevent chronic diseases. Nutrient-dense foods, such as fruits, vegetables, whole grains, lean protein, and healthy fat sources, deliver essential micronutrients, fiber, and bioactive compounds while minimizing caloric intake. This chapter reviews various ND scoring models, including the nutrient density scores, nutrient-rich food index, aggregate nutrient density index, nutrients-to-calorie ratio, new hybrid nutrient density score, and so on, that provide frameworks for ranking foods based on their nutrient content. These methods consider beneficial nutrients like vitamins and minerals while penalizing unhealthy components such as free sugar/added sugars, cholesterol, and saturated fats/trans fats. Advances in ND evaluation have fostered consumer awareness, influenced food labeling policies, and guided dietary recommendations to prevent NCDs. However, challenges persist, including inconsistencies among scoring systems, limited consideration of nutrient bioavailability, and oversights of complex food matrices. Despite these limitations, ND scores offer practical applications in guiding food choices, dietary management, informing public health policies, and improving food industry practices.