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Development of nitrogen use efficient (NUE) rice varieties is important for the sustainability of environmental-friendly and economical agricultural practices. Genotypic variation for NUE has been reported in rice, and several genetic sources have been identified. Mechanisms of nitrogen metabolism and traits/parameters associated with NUE have been extensively studied in rice. Several rice bi-parental mapping populations were evaluated and ∼200 quantitative trait loci (QTL) were identified for N metabolism and related traits. Recently, the association-mapping approach is also being adapted for identifying genomic regions and candidate genes for NUE in rice. Many known candidates genes associated with N metabolism in rice have been studied for their expression in genotypes with varying degrees of response to differential nitrogen application. Transcriptome analyses of various rice tissues grown under differential nitrogen levels have shown numerous differentially expressed genes (DEGs), and interesting families and pathways of genes have been identified. A strategy of maximum uptake, utilization, and remobilization to realize yield under optimum N input has been suggested for the development of rice varieties with NUE.NICR