Amino acids are building blocks of protein. More than 300 amino acids have been described, but only 20 amino acids take part in protein synthesis. All twenty amino acids did not appear simultaneously in nature. Instead some of them appeared early, while others were added into the genetic code later. It is necessary to take them in the diet because their deficiency results in decrease formation of protein that ultimately leads to disease condition. In this article, amino acids, its functions and associated diseases have been elaborated.