Habitual short sleep duration is consistently associated with weight gain and increased risk for obesity. The objective of this dissertation was to elucidate how chronic sleep restriction impacts components of energy balance, namely, weight gain, energy intake, and energy expenditure. Healthy adults (21-50 y) participated in controlled isolated laboratory protocols for 14-18 days and were randomized to either an experimental condition (baseline sleep followed by sleep restriction [5 consecutive nights of 4 hours time-in-bed [TIB] per night] and recovery sleep) or control condition (no sleep restriction: 10 hours TIB per night for all nights). Sleep-restricted subjects exhibited significant weight gain, increased caloric intake, greater consumption of fat, delayed meal timing and decreased resting metabolic rate (the largest component of energy expenditure) during sleep restriction but these changes returned to baseline levels after one night of recovery sleep (12 hours TIB). Control subjects did not exhibit a significant change in weight, caloric intake or resting metabolic rate across corresponding protocol days. Notably, there were significant gender and race differences in the energy balance response to sleep restriction. Men gained more weight, increased caloric intake to a greater degree during sleep restriction and consumed a larger percentage of calories during late-night hours than women. Relative to Caucasians, African Americans consumed a comparable amount of calories during baseline and sleep restriction but exhibited marked energy expenditure deficits after baseline sleep, sleep restriction and recovery sleep, and gained more weight during the study. In the largest, most diverse healthy sample of adults studied to date under controlled laboratory conditions, sleep restriction promoted weight gain and positive energy balance. Collectively, these results highlight the importance of obtaining sufficient sleep for regulating energy balance and maintaining a healthy weight, particularly in men and African Americans.