This chapter discusses acoustic rhinometry and objective measures of nasal airway obstruction, where nasal cycle is the physiologic alteration in nasal congestion on opposing sides of the nose, resulting in similar airflow, resistance, as well as amplitude. Nasal congestion or fullness appears to be the most bothersome symptom in patients with allergic rhinitis. Neurogenic causes occur via the trigeminal nerve as evidenced by the topical application of menthol, camphor, as well as other irritants resulting in an increase in the sensation of nasal patency. Acoustic rhinometry is the most commonly utilized objective test for the nasal airway. Nasal flow can either be turbulent or laminar. Nasal resistance is related to the nasal flow as well as to the pressure. Nasopharyngeal pressure changes between inspiration and hence leads to nasal airflow. In the active technique, the patient breathes through one nostril while the contralateral nasal pressure is assessed.