<p>Sleep is vital for human health, affecting nearly all body systems and tissues. Sleep is closely related to the release of certain chemicals in several regions of the brain. These chemicals include commonly known neurotransmitters and hormones such as acetylcholine, dopamine, epinephrine, GABA, glutamate, histamine, norepinephrine, serotonin, growth hormone, orexin, melatonin, and cortisol. Neurotransmitters and hormones are responsible for maintaining a balance between the sleep-promoting and wake-promoting regulation of sleep, and sleep stages have specific biochemical correlations. However, other chemicals such as adenosine, ATP, cytokines, galanin, and melanin-concentrating hormone also play a significant role in the regulation of sleep. The purpose of this article is to explore the biochemistry of normal sleep. It focuses on several key chemicals that play a role in normal sleep, namely the brain regions they are involved with, the stages of sleep they affect, the biochemical pathways and mechanisms by which they function, their downstream effects on the body, and the sleep disorders they are linked with.</p>