Cannabis and its pharmacologically active constituents, phytocannabinoids, have long been reported to have multiple medicinal benefits. One association often reported by users is sedation and subjective improvements in sleep. To further examine this association, we conducted a critical review of clinical studies examining the effects of cannabinoids on subjective and objective measures of sleep. PubMED, Web of Science, and Google Scholar were searched using terms and synonyms related to cannabinoids and sleep. Articles chosen included randomized controlled trials and open label studies. The Cochrane risk of bias tool was used to assess the quality of trials that compared cannabinoids with control interventions. The current literature focuses mostly on the use of tetrahydrocannabinol (THC) and/or cannabidiol (CBD) in the treatment of chronic health conditions such as multiple sclerosis, posttraumatic stress disorder (PTSD), and chronic pain. Sleep is often a secondary, rather than primary outcome in these studies. Many of the reviewed studies suggested that cannabinoids could improve sleep quality, decrease sleep disturbances, and decrease sleep onset latency. While many of the studies did show a positive effect on sleep, there are many limiting factors such as small sample sizes, examining sleep as a secondary outcome in the context of another illness, and relatively few studies using validated subjective or objective measurements. This review also identified several questions that should be addressed in future research. These questions include further elucidation of the dichotomy between the effects of THC and CBD, as well as identifying any long-term adverse effects of medicinal cannabinoid use. (PsycINFO Database Record (c) 2019 APA, all rights reserved).