Dietary proteins are digested in the intestine to amino acids and are absorbed by an active transport mechanism. The first step in amino acid degradation is the removal of their α-amino groups by transamination and deamination in the form of ammonia. Ammonia is converged into urea. Inherited disorders of the urea cycle cause hyperammonemia and can lead to brain damage. After removal of amino groups, the carbon skeletons of amino acids are converted into pyruvate, acetyl CoA, acetoacetate or an intermediate of the citric acid cycle. Most amino acids are solely glucogenic, two are solely ketogenic and a few are both glucogenic and ketogenic. Human can synthesize only 10 of the 20 standard amino acids required for the protein synthesis; the other 10 are considered essential amino acids for the diet. In this chapter metabolism of each individual amino acid is discussed. Inborn errors in amino acid degradation pathways can lead to hyperoxaluria, methionine degradation can lead to homocystinuria, branched chain amino acid can lead to maple syrup urine disease, and phenylalanine and tyrosine degradation can lead to phenylketonuria, alkaptonuria and albinism.