Insomnia disorder and obstructive sleep apnea are the two most common sleep disorders among adults. Historically, these conditions have been conceptualized as orthogonal, or insomnia has been considered a symptom of sleep apnea. Insomnia researchers have sought to exclude participants at risk for sleep-related breathing disorders (SRBD), and vice versa. In recent years, however, there has been a growing recognition of co-occurring insomnia disorder and SRBD and interest in the prevalence, consequences, and treatment of the two conditions when they co-occur. Although plagued by inconsistent diagnostic criteria and operational definitions, evidence from clinical and research samples consistently suggests high rates of comorbidity between the two disorders. More important, insomnia disorder and SRBD have additive negative effects. To date, only a few studies have explored the combined or sequential treatment of the conditions. Results support the importance of an integrated, interdisciplinary approach to sleep medicine. This article reviews the empirical literature to date and provides clinical recommendations as well as suggestions for future research.