Sleep-disordered breathing and insomnia are the most common of the sleep disorders. Both these diseases are well defined, diagnosed and managed as per the current guidelines. The initial isolated reports of an overlap of these two diseases were published in the eighties. With newer studies post-2001, the existence of the comorbid obstructive sleep apnea (OSA) and upper airway resistance syndrome (UARS) with insomnia has been increasingly recognized. This disease entity has been referred with diverse unstandardized terminologies. UARS is a variant nomenclature of OSA as per International Classification of Sleep Disorders- third edition (ICSD-3). We hereby address it as the OSA–insomnia overlap syndrome throughout the text and review literature. Alike the ununiform terminology, there is lack of clear textbook/guideline definitions, diagnosis, and management of the OSA–insomnia overlap syndrome. Both have an interlinked pathophysiology. The clinical features and evaluation of the OSA–insomnia overlap syndrome share similarities to the diseases in isolation with exacerbation of overlapping features. An active search for the diagnosis of the overlap syndrome in patients visiting the sleep apnea clinic and insomnia clinic is mandatory as the identification helps in optimizing the management and difficulties in poor responders/ failures. Continuous positive airway pressure (CPAP) therapy with cognitive/behavior therapy for insomnia (CBTi) is the treatment of choice. A lot is yet to surface in the research of the OSA–insomnia overlap syndrome.