Sleep hygiene (SH) refers to a list of behaviors, environmental conditions, and other sleep-related factors that can be adjusted as a stand-alone treatment or component of multimodal treatment for patients with insomnia. This paper presents a review of SH, how this concept has been applied and often modified over the past 24 years, and how it relates to the modern sleep disorder nosology, particularly Inadequate Sleep Hygiene. Although a recognized and commonly utilized treatment option, there is no absolute consensus about which steps must be included to constitute SH treatment, and there is much overlap between SH and other cognitive-behavioral treatments for insomnia such as Stimulus Control Procedures and Sleep Restriction Therapy. The literature on the effects of manipulations of individual components of SH under experimental conditions (e.g. effects of presleep alcohol or caffeine intake) in normal sleepers show mixed results. Empirical data demonstrating the role of poor SH as a contributor to insomnia, or showing that good SH improves sleep in patients with insomnia, is not available. Instead of evaluating the impact of a comprehensive list of SH recommendations, a focus on guidelines for use of individual rules is needed.