This review provides an overview of the current understanding of the neural systems involved in regulating wakefulness, non-rapid eye movement sleep (NREMS), and rapid eye movement sleep (REMS) in mammals. Specifically, we focus on the anatomical connections between the subiculum, a component of the hippocampal formation, and the regions responsible for regulating the sleep-wake cycle. The subiculum exhibits direct connections with key areas involved in sleep regulation, such as the lateral hypothalamus, tuberomammillary nucleus, basal forebrain, ventrolateral preoptic nucleus, ventrolateral tegmental area, and suprachiasmatic nucleus. Additionally, second-order projections from the subiculum are received by the laterodorsal tegmental nucleus and locus coeruleus, suggesting potential involvement of the subiculum in the regulation of circadian rhythms, particularly the circadian sleep-wake cycle. We also discuss alterations in the subiculum observed in individuals with sleep disorders and sleep-deprived mice, underscoring the significance of investigating neuronal communication between the subiculum and pathways promoting both sleep and wakefulness.