In the 21st century nutrient efficient plants will play a greater role in increasing crop yields. Limited land and water resources, higher cost of inorganic fertilizers inputs, and declining crop yields in the future will create greater demand for cultivars with higher nutrient efficiency. Furthermore, at least 60% of the arable land in the world has mineral deficiencies or elemental toxicity problems. About 50% of the world population suffer from micronutrient deficiencies. In addition, increasing demand for food and fiber by an ever increasing world population further enhances the importance of growing nutrient efficient plants. Nutrient efficient plants are defined as those plants which produce higher yields per unit of nutrient applied or uptake compared to other plants (standards) under similar agroecological conditions. During the last three decades, plenty of research has been conducted to identify nutrient efficient plant species or genotypes within species and to understand mechanisms of nutrient efficiency in crop plants. However, so far the success of releasing nutrient efficient cultivars is limited. The main reason for limited success in this area is lack of understanding of plant genetics and its interactions with environmental variables on nutrient use efficiency in plants. There is need for multidisciplinary efforts of plant breeders, soil scientists, physiologists and agronomists to breed nutrient efficient cultivars that are suitable to various agroecological regions of the world. Hence, during 21st century agricultural scientists have tremendous challenges as well as opportunities to develop nutrient efficient crop plants. During the 20th century, breeding for nutritional traits has been proposed as a strategy to improve the efficiency of fertilizer use or to obtain higher yields in low input agricultural systems. This strategy should continue to receive top priority during the 21st century for developing nutrient efficient crop cultivars. This paper emphasizes the importance of nutrient efficient plants in modern agriculture, definitions, available methods of calculating nutrient use efficiency, mechanisms for nutrient uptake and use efficiency and breeding strategies to improve nutrient use efficiency in crop plants.