The black-naped monarch or black-naped blue flycatcher (Hypothymis azurea ) is a slim and agile passerine bird belonging to the family of monarch flycatchers found in southern and south-eastern Asia. They are sexually dimorphic, with the male having a distinctive black patch on the back of the head and a narrow black half collar ("necklace"), while the female is duller with olive brown wings and lacking the black markings on the head. They have a call that is similar to that of the Asian paradise flycatcher, and in tropical forest habitats, pairs may join mixed-species foraging flocks. Populations differ slightly in plumage colour and sizes.
The adult male black-naped monarch is about 16 cm long, and is mainly pale azure blue apart from a whitish lower belly. It has a black nape and a narrow black gorget. The female is duller and lacks the black markings. Its wings and back are grey-brown. However, several geographically separated breeding populations differ in the extent and shade of markings. The Indian peninsula has subspecies H. a. styani (which subsumes H. a. sykesi of Stuart Baker), in which males have very distinct black markings and a whitish abdomen. Males of the Sri Lankan race H. a. ceylonensis lack the black nape and gorget and the shade is more purplish. The subspecies of the Andaman Islands, H. a. tytleri, has the underparts blue grey. The form on Car Nicobar Island, H. a. idiochroa, has a greyish white belly, while H. a. nicobarica from the southern Nicobars has a smaller and finer bill. The colour of the gape is yellowish to green.