A nasal delivery device for delivering substance to a nasal airway of a subject, comprising: a mouthpiece (119; 219; 319; 419; 519; 619; 919) through which the subject in use exhales to cause closure of the oropharyngeal velum of the subject; a nosepiece (117; 217; 317; 417; 517; 617; 917) for fitting to a nostril of a subject, the nosepiece (117; 217; 317; 417; 517; 617; 917) including a nozzle (149; 249; 349; 459; 549; 649; 949) through which substance is in use delivered to the nasal airway; and a body member (121; 223; 321; 421; 521; 621; 921) which receives a substance supply unit (120; 220; 320; 420; 520; 620; 920), wherein the body member (121; 223; 321; 421; 521; 621; 921) includes an inlet (325; 525; 625; 925) which is in fluid communication with the mouthpiece (119; 219; 319; 419; 519; 619; 919) and an outlet (327; 527; 627; 927) which is in fluid communication with the nosepiece (117; 217; 317; 417; 517; 617; 917); characterized by: a manually-actuatable substance supply unit (120; 220; 320; 420; 520; 620; 920) for delivering substance through the nozzle (149; 249; 349; 459; 549; 649; 949) of the nosepiece (117; 217; 317; 417; 517; 617; 917), wherein the substance supply unit (120; 220; 320; 420; 520; 620; 920) comprises a body part (355; 655; 955) which is movable from a first, rest position to a second, actuated position on manual actuation of the substance supply unit (120; 220; 320; 420; 520; 620; 920), and the inlet (325; 525; 625; 925) of the body member (121; 223; 321; 421; 521; 621; 921) is opened when the body part (355; 655; 955) of the substance supply unit (120; 220; 320; 420; 520; 620; 920) is moved to the actuated position, thereby providing for an air flow through the nosepiece (117; 217; 317; 417; 517; 617; 917) simultaneously with manual actuation of the substance supply unit (120; 220; 320; 420; 520; 620; 920). a mouthpiece (119; 219; 319; 419; 519; 619; 919) through which the subject in use exhales to cause closure of the oropharyngeal velum of the subject; a nosepiece (117; 217; 317; 417; 517; 617; 917) for fitting to a nostril of a subject, the nosepiece (117; 217; 317; 417; 517; 617; 917) including a nozzle (149; 249; 349; 459; 549; 649; 949) through which substance is in use delivered to the nasal airway; and a body member (121; 223; 321; 421; 521; 621; 921) which receives a substance supply unit (120; 220; 320; 420; 520; 620; 920), wherein the body member (121; 223; 321; 421; 521; 621; 921) includes an inlet (325; 525; 625; 925) which is in fluid communication with the mouthpiece (119; 219; 319; 419; 519; 619; 919) and an outlet (327; 527; 627; 927) which is in fluid communication with the nosepiece (117; 217; 317; 417; 517; 617; 917); characterized by: a manually-actuatable substance supply unit (120; 220; 320; 420; 520; 620; 920) for delivering substance through the nozzle (149; 249; 349; 459; 549; 649; 949) of the nosepiece (117; 217; 317; 417; 517; 617; 917), wherein the substance supply unit (120; 220; 320; 420; 520; 620; 920) comprises a body part (355; 655; 955) which is movable from a first, rest position to a second, actuated position on manual actuation of the substance supply unit (120; 220; 320; 420; 520; 620; 920), and the inlet (325; 525; 625; 925) of the body member (121; 223; 321; 421; 521; 621; 921) is opened when the body part (355; 655; 955) of the substance supply unit (120; 220; 320; 420; 520; 620; 920) is moved to the actuated position, thereby providing for an air flow through the nosepiece (117; 217; 317; 417; 517; 617; 917) simultaneously with manual actuation of the substance supply unit (120; 220; 320; 420; 520; 620; 920). a manually-actuatable substance supply unit (120; 220; 320; 420; 520; 620; 920) for delivering substance through the nozzle (149; 249; 349; 459; 549; 649; 949) of the nosepiece (117; 217; 317; 417; 517; 617; 917), wherein the substance supply unit (120; 220; 320; 420; 520; 620; 920) comprises a body part (355; 655; 955) which is movable from a first, rest position to a second, actuated position on manual actuation of the substance supply unit (120; 220; 320; 420; 520; 620; 920), and the inlet (325; 525; 625; 925) of the body member (121; 223; 321; 421; 521; 621; 921) is opened when the body part (355; 655; 955) of the substance supply unit (120; 220; 320; 420; 520; 620; 920) is moved to the actuated position, thereby providing for an air flow through the nosepiece (117; 217; 317; 417; 517; 617; 917) simultaneously with manual actuation of the substance supply unit (120; 220; 320; 420; 520; 620; 920).