A nasal delivery device for and a method of delivering substance to a nasal airway of a subject, the nasal delivery device including: a mouthpiece (519) through which the subject in use exhales to cause closure of the oropharyngeal velum of the subject; a nosepiece (517) for fitting to a nostril of a subject, the nosepiece including a nozzle (549) through which substance is in use delivered to the nasal airway; and a manually-actuatable substance supply unit (520) for delivering substance through the nozzle of the nosepiece.