An exhalation breath-actuated nasal delivery device for and a method of delivering a substance to a nasal cavity of a subject, the delivery device comprising: a nosepiece (40) for fitting to a nostril of a subject; a mouthpiece (42) through which the subject in use exhales; and delivery unit (64), as one of a mechanical delivery pump (66) or a nebulizer (115), for delivering a substance to the nosepiece (40); and an actuation mechanism (74) for actuating the delivery unit in response to oral exhalation through the mouthpiece, and preferably when at least one or both of the pressure at or the flow rate through the nosepiece exceeds a predetermined threshold.