Sleep plays a vital role in good health and well-being throughout our life. Getting enough quality sleep at the right times can help protect our mental health, physical health, quality of life, and safety. In this Masterclass, we discuss how sleep is important for learning and memory, alertness, sustained attention and cognitive flexibility, how chronic short sleep reduces alertness and cognitive flexibility and how this is cumulative, and how attempting to recover our sleep debt on weekends still leaves us with attention deficits.