Background: Chronic Fatigue Syndrome (CFS) affects 0.23–2.6% of the adult population. Sleep-related complaints are amongst the most frequently reported symptoms in these patients. Although a biopsychosocial model of CFS offers a plausible framework for understanding the condition, the role of sleep and how it functions within this model remains unclear. Purpose: This narrative review describes the findings of studies of sleep in CFS and considers the reasons behind the diversity of results. The review also discusses the difficulties that exist in establishing relationships between sleep, behaviour, cognition, physiology, and the physical symptoms of CFS. Methods: A search of Medline for the terms “CFS,” “chronic fatigue syndrome,” AND “sleep” was performed to identify articles concerning sleep and CFS from 1988 to the present. Results: Subjective sleep dysfunction was frequently reported in the CFS sleep studies. However, objective sleep research in CFS has shown no consistent picture of sleep disturbance, particularly with regard to polysomnography. This may be attributable to the heterogeneity of sleep phenotypes in the CFS population as well as the variability in sleep assessment protocols, case definitions, and exclusion criteria used across studies. Conclusions: Given the high prevalence of disturbed sleep in this population in combination with inconsistent findings, exploration of new protocols for the objective assessment of sleep in CFS (e.g., three-night PSG protocol) is recommended. Understanding the distinct sleep characteristics in this population could serve to improve insight into perpetuating factors of CFS symptoms which is relevant for diagnosis and therapy.