Sleep is a vital process to the overall health of any individual. It is fundamental for many physiological processes, and higher cognitive functions like memory, learning and emotions. In addition, it assists in some metabolic and immune processes, among other functions.Sleep architecture is divided in two stages, in NREM and REM sleep. The difference between them is the brain activity, ocular movements, the dynamism and modulation of different systems, neurotransmitter release, and some endogenous substances.In this paper, we will recapitulate the main modulatory molecules involved in the regulation of this complex and fundamental activity.