The orexins/hypocretins are novel neuropeptides synthesized by neurons whose cell bodies are located in the lateral hypothalamus. Although these neurons are few in number, they send projections widely throughout the central nervous system (Kilduff & Peyron, 2000). There has been great excitement about the orexins/hypocretins from both the scientific and medical community. These peptides are remarkable in that they were discovered using state-of-the-art molecular techniques before their physiological actions were studied. Furthermore, there has been an exponential progress in our scientific knowledge of these peptides culminating in the orexins/hypocretins being linked to the sleep disorder, narcolepsy. With the importance of the orexins/hypocretins in sleep and arousal being increasingly recognized, it is likely that these peptides are altered by or contribute to several medical and psychiatric disorders.