Zebrafish (Danio rerio), a small prolific rapidly-developing diurnal vertebrate, shows behavioral, physiological, and pharmacological characteristics of mammalian sleep. Zebrafish brain has well-developed neuronal structures and neurochemical systems that are known to be necessary and sufficient for sleep regulation in other vertebrate species. Rich behavioral repertoire in zebrafish permits investigation of the effects of sleep and sleep deprivation on cognitive functions and performance. Sensitivity of this fish to hypnotic agents helps in designing high throughput screens for new hypnotic medications, evaluation of their efficacy, and potential side effects. The optical transparency of larval zebrafish and intracellular fluorescent markers of calcium responses available make it possible to visualize neuronal activity with single cell resolution in a behaving fish. Given the accumulated experience in conducting large-scale genetic screens in zebrafish, multiple available mutant phenotypes, and advanced genetic and physical maps of this vertebrate, zebrafish is an excellent model for studying the enigmatic basic sleep function and mechanisms of sleep regulation.