Nurses are accustomed to helping others with their sleep problems and dealing with issues such as pain that may delay or interrupt sleep. However, they may be less familiar with what constitutes a healthy night’s sleep. This article examines what is known about the process and purpose of sleep, and examines the ways in which factors that promote wakefulness and sleep combine to help establish a normal circadian rhythm. Theories relating to the function of sleep are discussed and research is considered that suggests that sleep deficit may lead to metabolic risks, including heart disease, obesity, type 2 diabetes mellitus and several types of cancer.