A breath-actuated nasal delivery device, comprising: a mouthpiece through which a user in use exhales to actuate the delivery device a nosepiece for fitting to a nostril of the user through which a substance is in use delivered a substance supply unit actuatable to deliver a dose of a substance through the nosepiece a loading unit operable to load the substance supply unit with an actuation force and a release mechanism for enabling actuation of the substance supply unit in response to exhalation by the user through the mouthpiece wherein the release mechanism comprises a locking unit which is movable: between a locking configuration in which the substance supply unit is locked in a non-actuated position when loaded by the loading unit and a release configuration in which the substance supply unit is actuatable by the loading unit, and a trigger member for releasing the locking unit from the locking configuration to the release configuration in response to exhalation by the user through the mouthpiece and thereby enabling actuation of the substance supply unit.
