The following work has been performed: - Work with the simulation programmet SWP (Sleep-Wake-Predictor) - Field study and a simulator study on watch systems - Analysis of data from a study on partial sleep deprivation - Analysis of data from a study on total sleep deprivation for 24 hours - Studies on social interaction as countermeasures against sleep deprivation - Planning of a study on necessary recovery from sleep deprivation of different durations - Studies on long flights The following studies are presented: 1. Models for prediction of sleep/wakefulness 2. Partial sleep deprivation and cognitive performance 3. Total sleep deprivation and learning 4. Long flights