A delivery device for and method of delivering substance to a nasal airway of a subject, the delivery device comprising: at least one nosepiece unit (21) for insertion into one nasal cavity of a subject and comprising a nosepiece (25) for fitting to the respective nostril of the subject; and at least one delivery unit (23) which is operative to deliver a substance through the at least one nosepiece unit into the one nasal cavity of the subject, wherein the at least one delivery unit includes a substance supply unit (27) for delivering a substance and an actuation unit (29) which is operable to actuate the substance supply unit, either automatically or manually, in response to nasal exhalation or at least attempted nasal exhalation by the subject.