A nasal delivery device for delivering a substance to the nasal airway of a subject, comprising: a closure unit for causing the closure of the oropharyngeal velum of the subject and a delivery unit (22) for delivering a substance to one of the nostrils of the subject, wherein the delivery unit (22) comprises a nosepiece (30) which includes an outlet through which the substance is in use delivered to the one nostril and a sealing member for providing a fluid tight seal between the outlet and the one nostril.
