Why We Sleep: Unlocking the Power of Sleep and Dreams by Matthew Walker, PhD, is a popular science book that argues sleep is a fundamental pillar of health, not a luxury, and that modern society faces a "sleep loss epidemic". Walker, a neuroscientist, explains the crucial functions of sleep for physical and mental well-being, linking insufficient sleep to numerous health problems like Alzheimer's, cancer, diabetes, and impaired memory, while offering practical advice on how to improve sleep quality.