Sleep is a basic need. Mounting evidence suggests this is particularly true during adolescence, a developmental period involving substantial changes in the brain regions supporting cognition, learning, and emotion. Although sleep loss is a normative psychosocially and biologically driven developmental process, it occurs alongside behaviors that characterize adolescence, including deepening cognitive sophistication, improved emotion regulation, and intensifying social cognition, calling into question how sleep may impact these developmental milestones. This review synthesizes growing research aimed at addressing this timely question. It presents evidence that neurodevelopmental changes in brain structure, function, and sleep physiology mechanistically link the relationship between sleep and cognitive ability. Copyright © 2019 Elsevier Ltd. All rights reserved.