Ketogenic diet (KD) has for a long time been known as an effective treatment for medically intractable epilepsy. However, the underlying mechanism is still unknown. Recent work indicates, that several mechanisms exist for KD, including neurotransmitter regulation, glucose restriction, effects of fatty acids, altered mitochondrial function and mammalian target of rapamycin pathway. Revealing the mechanisms of KD provides a better insight in the pathophysiology of epilepsy and helps the development of new treatments of epilepsy and other neurological disorders.