Monoamine oxidases (MAO) are a family of enzymes that catalyze the oxidation of monoamines. They are found bound to the outer membrane of mitochondria in most cell types in the body. They belong to the protein family of flavin-containing amine oxidoreductases. Monoamine oxidases catalyze the oxidative deamination of monoamines. Oxygen is used to remove an amine group from a molecule, resulting in the corresponding aldehyde and ammonia. Monoamine oxidases contain the covalently bound cofactor FAD and are, thus, classified as flavoproteins. Because of the vital role that MAOs play in the inactivation of neurotransmitters, MAO dysfunction is thought to be responsible for a number of psychiatric and neurological disorders. MAO-A inhibitors act as antidepressant and antianxiety agents, whereas MAO-B inhibitors are used alone or in combination to treat Alzheimer’sand Parkinson’s diseases.