David Bowie, Ozzy Osbourne and Tupac sang about them: Changes. Change is an apt descriptor of adolescence. With the onset of puberty, adolescents rapidly journey through physical changes in height and shape, and through neurological developments that herald cognitive, emotional, and social transitions, developing from the parented children in the back seats of cars to the soon-to-be- adults behind the literal and metaphorical steering wheels. And at the end of the day, they lay themselves down to sleep. This brings us to the focus of this special issue in the Journal of Adolescence. Aside from the rapid changes that occur during infancy, adolescence is the second-most dynamic period of development for sleep. Changes in circadian rhythms and sleep homeostatic pressure lie behind the changes seen in the timing of sleep, leading to sleep duration deficits for most adolescents. These deficits have important implications for adolescents’ functioning, as documented in this issue and other research.