This review consolidates research employing human correlational and experimental work across brain and body with experimental animal models to provide a more complete representation of how circadian rhythms influence almost all aspects of life. In doing so, we will cover the morphological and biochemical pathways responsible for rhythm generation as well as interactions between these systems and others (e.g., stress, feeding, reproduction). The effects of circadian disruption on the health of humans, including time of day effects, cognitive sequelae, dementia, Alzheimer's disease, diet, obesity, food preferences, mood disorders, and cancer will also be discussed. Subsequently, experimental support for these largely correlational human studies conducted in non-human animal models will be described.