The Red-flanked Bluetail (Tarsiger cyanurus) is a small passerine bird that was formerly classed as a member of the thrush family Turdidae, but is now more generally considered to be an Old World flycatcher, Muscicapidae. It, and related species, are often called chats.

It is a migratory insectivorous species breeding in mixed coniferous forest with undergrowth in north Asia to the Himalayas and western China. Red-flanked Bluetails winter in southeast Asia.

The species' range is slowly expanding westwards through Finland. It is a very rare but increasing vagrant to western Europe, and there have been a few records in westernmost North America.

The Red-flanked Bluetail nests near the ground, laying 3-5 eggs which are incubated by the female.

It is slightly larger in size than the European Robin. As the name implies, both sexes have a blue tail and reddish flanks. The adult male has dark blue upperparts and white underparts. Females are plain brown above and have a dusky breast.

The male sings its melancholy trill from treetops. Its call is a typical chat "tacc" noise.