Nucleotides are phosphate esters of nucleosides that contain a sugar linked through a glycosidic linkage with purine and pyrimidine bases. Purine and pyrimidine nucleotides are major components of the cells that make up the monomeric units of DNA and RNA, and they function in all cellular processes. Biosynthesis, interconversion, catabolism and other aspects of nucleotide metabolism, along with various cellular roles of nucleotides, will be discussed, and the possible use of dietary sources of preformed purines and pyrimidines will be considered.