Military personnel of many professions, including health care workers, are routinely challenged with performing their duties during hours when the circadian rhythm is at its trough, namely, late night and early morning. Studies have shown that cognitive performance declines significantly during these hours. Although many pharmacologic agents have been studied in an attempt to find a safe medication to enhance alertness and cognitive function, no safe nonaddictive options have been identified. Modafinil is a novel wakefulness-promoting agent that has been shown to improve cognitive performance and promote wakefulness among shift workers. This article reviews the studies on modafinil administration and cognitive performance as they relate to military operations and the provision of health care by sleep-deprived individuals.