Sleep is a complex physiological process and remain one of the great mysteries of science. Hypotheses for sleep include somatic, metabolic, cellular theories, as well as brain-specific functions such as synaptic plasticity, or synaptic downscaling. Over the past 10 years, genetics provides a new way to address the regulation and function of sleep. Major findings include the identification of loci that make quantitative contributions to sleep characteristics and variability. From Drosophila, zebrafish, and worms to mammalian model organisms, some genes implicated in sleep homeostatic regulation have beeen identified.