Sleep loss has tremendous societal implications associated with lost productivity, injuries, accidents, and excessive financial costs. This chapter discusses the nature of sleep loss and sleep disorders and their implications for human health and well-being. It reviews the epidemiological and societal consequences of sleep disorders and discusses diagnostic classification systems and their implications for nursing. Sleep loss results from obtaining less sleep than needed and/or fragmented sleep that leads to deprivation of specific sleep stages even in the presence of adequate total sleep. However, chronic sleep deprivation is endemic and contributes to pathophysiology, daytime dysfunction, fatigue, sleepiness, morbidity, injury, mortality, and poor quality of life. Sleep loss, its consequences, and strategies to prevent and/or treat it are important thematic underpinnings in these narratives. Proficiency in the use of relevant sleep diagnostic classification systems is necessary to interdisciplinary collaboration and sleep diagnosis and treatment.