One of the most significant and dangerous social and public health problem facing adolescents today is sleep loss. Chronic partial sleep deprivation has achieved epidemic proportions in youth, with approximately 80% of teens not getting the needed amount of nightly sleep. Despite the alarmingly high rates of sleep deprivation in teens, its impact on daytime function, including sleepiness, mood, and cognition remain poorly understood. To address this knowledge gap, we intend to examine sleep, neuropsychological (NP) performance, and mood in the natural environment in 40 healthy adolescents (ages 16-18; 50% female). Each teen will undergo 2 different sleep conditions: 1) an “extended” sleep period consisting of 5 consecutive days of 10-10.5 hrs in bed/night; and 2) a “typical” sleep period consisting of 5 consecutive days of 7.5-8.0 hrs in bed/night (the common sleep duration for this age group). The former will provide sleep satiation or optimal biological sleep need (for this age group), while the latter will result in an insufficient amount of sleep. Each teen will be randomly assigned to one of the sleep conditions, followed by a 2-week “recovery” period, and then the other sleep condition. Sleep testing will include continuous actigraphic monitoring throughout each sleep protocol and one overnight polysomnography recording at the beginning of the study to rule out any sleep disorders. Following the last night of each sleep condition, teens will undergo a battery of standardized NP tests to examine performance in cognitive areas previously found to be related sleep deprivation, including verbal learning, memory, processing speed and attention, inhibition, working memory, and executive function. Findings will increase our knowledge of the correlates of sleep loss in teens and will be useful public policy and education data. Furthermore, it will allow the researcher the opportunity to continue her line of research and reintegrate into the host country.