Disturbances in sleep associated with sleep deprivation, disorders in circadian rhythms, and sleep-disordered breathing are common in critical care settings and may have a significant impact on physiologic, behavioral, and functional outcomes, as well as patient satisfaction and utilization of healthcare resources. Despite growth in awareness of the potential importance of sleep in the critical setting over the past 30 years, many questions about the nature of sleep, the predictors and consequences of sleep disturbance, and the efficacy of sleep promotion interventions in critically ill patients remain unanswered. Most of the studies of sleep in critical care settings have used small, nonrandom samples and descriptive or explanatory designs; many have not considered multifactorial explanatory variables; and clinical trials are rare. These gaps in quantity and quality of research findings are barriers to the delivery of evidence-based sleep promotion interventions and may be partially explained by conceptual and methodological challenges associated primarily with the nature of sleep measurement and characteristics of critically ill patients and the critical care environment. This article will explore these concerns and propose strategies to deal with them. Research exemplars from the literature will be used to illustrate key points.