Smoking and OSA are widely prevalent and are associated with significant morbidity and mortality. It has been hypothesized that each of these conditions adversely affects the other, leading to increased comorbidity while altering the efficacy of existing therapies. However, while the association between smoking and OSA is plausible, the evidence is less than conclusive. Cigarette smoking may increase the severity of OSA through alterations in sleep architecture, upper airway neuromuscular function, arousal mechanisms, and upper airway inflammation. Conversely, some evidence links untreated OSA with smoking addiction. Smoking cessation should improve OSA, but the evidence to support this is also limited. This article reviews the current evidence linking both conditions and the efficacy of various treatments. Limitations of the current evidence and areas in need of future investigation are also addressed.