A nasal delivery device for and method of delivering substance to a nasal airway of a subject, the delivery device comprising: a nosepiece (117) for fitting to a nasal cavity of a subject; a mouthpiece (119) into which the subject in use exhales; a delivery unit, which comprises an actuation part which is manually displaceable to actuate the delivery unit to deliver substance from the nosepiece; and a valve assembly (127) which is fluidly connected to the nosepiece and the mouthpiece, wherein the valve assembly comprises a body element (128) and a valve element (131) which is movably disposed to the body element between closed and open configurations by manual displacement of the actuation part of the delivery unit to provide for an air flow through the nosepiece simultaneously with delivery of substance.