The orexin/hypocretin system is a key neuropeptide system involved in regulating vigilance and stress responses. This review discusses the role of orexins in various physiological and behavioral processes, including stress, fear, anxiety, and learning. The orexin system is composed of two neuropeptides, orexin-A and orexin-B, and two receptors, OX1R and OX2R. These neuropeptides are involved in regulating arousal, sleep-wake cycles, and circadian rhythms. The orexin system also plays a role in food intake, metabolism, and thermoregulation. The system is closely linked to the central oscillator, which regulates circadian activities. Orexins are also involved in the regulation of the stress response, with orexin-A and orexin-B playing different roles in this process. The orexin system is essential for maintaining vigilance and has been implicated in disorders such as narcolepsy and cataplexy. The system is also involved in the regulation of anxiety and reward-related learning processes. Orexins are prime examples of hedonistic neuropeptides and are involved in the control of natural rewards such as food and reproduction. The orexin system interacts with other neuropeptide systems, such as the MCH, NPY, and ghrelin systems, to regulate various physiological processes. The orexin system has therapeutic potential in the treatment of sleep disorders and other neurological conditions. The system is also involved in the regulation of pain and mood, and its dysfunction is associated with various neurological and psychiatric disorders. The orexin system is a complex network that plays a crucial role in maintaining homeostasis and adapting to stress.The orexin/hypocretin system is a key neuropeptide system involved in regulating vigilance and stress responses. This review discusses the role of orexins in various physiological and behavioral processes, including stress, fear, anxiety, and learning. The orexin system is composed of two neuropeptides, orexin-A and orexin-B, and two receptors, OX1R and OX2R. These neuropeptides are involved in regulating arousal, sleep-wake cycles, and circadian rhythms. The orexin system also plays a role in food intake, metabolism, and thermoregulation. The system is closely linked to the central oscillator, which regulates circadian activities. Orexins are also involved in the regulation of the stress response, with orexin-A and orexin-B playing different roles in this process. The orexin system is essential for maintaining vigilance and has been implicated in disorders such as narcolepsy and cataplexy. The system is also involved in the regulation of anxiety and reward-related learning processes. Orexins are prime examples of hedonistic neuropeptides and are involved in the control of natural rewards such as food and reproduction. The orexin system interacts with other neuropeptide systems, such as the MCH, NPY, and ghrelin systems, to regulate various physiological processes. The orexin system has therapeutic potential in the treatment of sleep disorders and other neurological conditions. The system is also involved in the regulation of pain and mood, and its dysfunction is associated with various neurological and psychiatric disorders. The orexin system is a complex network that plays a crucial role in maintaining homeostasis and adapting to stress.