This chapter discusses the neuroendocrine function changes in the context of the hypothalamic-pituitary-adrenal (HPA) axis, the somatotropin axis, the hypothalamic-gonadal (HPG) axes, and the orexin-hypocretin system. It describes the thyroid axis as well as relationships with prolactin. The chapter links changes in sleep with aging with changes in neuroendocrine systems with aging. Some age-associated changes in HPA axis activity correlate with similarly associated changes in sleep. There is an age-related change in GH secretion. The inverse relationship between Growth hormone-releasing hormone (GHRH) and slow wave sleep (SWS) as well as between corticotropin-releasing hormone (CRH) and GHRH provide the basis for influences of GHRH on sleep in aging. Gonadotropin-releasing hormone (GnRH) is produced and released in the hypothalamus. The hypocretin-orexin system is important for influencing many aspects of sleep-related brainstem nuclei activity. Thyroid-stimulating hormone (TSH) is secreted in a circadian-dependent pattern with peak levels occurring during sleep.