Selenium (SE) is an essential micronutrient fulfilling a number of biological roles, being integrated as selenocysteine in the primary structure of certain selenoproteins. The Selenocysteine is synthesized and inserted into proteins during the translational process of the RNAm by a mechanism which involves converting a stop codon for certain proteins into a meaningful codon. Only 25 genes encoding selenocysteine-incorporating proteins have been identified in the human genome. The selenoprotein families including glutathione peroxidase, iodothyronine deiodinase and thioredoxin reductases are known as enzymes engaged in redox processes. The selenoprotein P (SEPP1) is a hepatokine produced by the liver, an extracellular glycoprotein, which is not part of these families. The purpose of this Article is to present the form of distribution of selenium and its physiological role in the body.