Nasal obstruction whether partial or complete can influence the quality of sleep and has been strongly linked to the genesis of obstructed breathing during sleep (OBS). The relationship between nasal airflow and the process of upper airway collapse is complex. The first part of this article reviews the nasal anatomy with an emphasis on the sites of nasal obstruction, the effect of the nasal reflexes on the pulmonary system, and the pathophysiology of the development of OBS. The second part reviews the common causes of increased nasal resistance, the assessment of nasal passages, and the treatment options. This article also includes literature in support of and refuting the postulated mechanisms by which nasal obstruction can effect the respiratory system during sleep.