The long-tailed jaeger or long-tailed skua (Stercorarius longicaudus) is a seabird in the skua family Stercorariidae.

This species is unmistakable as an adult, with grey back, dark primary wing feathers without a white "flash", black cap and very long tail. Adults often hover over their breeding territories. Juveniles are much more problematic, and are difficult to separate from parasitic jaeger over the sea. They are slimmer, longer-winged and more tern-like than that species, but show the same wide range of plumage variation. However, they are usually colder toned than Arctic, with greyer shades, rather than brown.

This is the smallest of the skua family at 38–58 cm (15–23 in), depending on season and age. However up to 29 cm (11 in) of its length can be made up by the tail which may include the 15 cm (5.9 in) tail streamers of the summer adult. The wingspan of this species ranges from 102 to 117 cm (40 to 46 in) and the body mass is 230–444 g (8.1–15.7 oz).

When at sea, the long-tailed jaeger will catch fish and other small prey at the surface of the water. During the breeding season (summer in arctic regions, often in mountainous areas) it feeds mainly on lemmings near nesting sites. It will sometimes feed on insects and birds. Like other jaegers and skuas, it is also a kleptoparasite; chasing other seabirds to make them give up their food. This appears to be an important food source during the winter months, spent south of the equator. The bird species most commonly "robbed" this way by the long-tailed jaeger are arctic terns (Sterna paradisaea) and sabine's gulls (Larus sabini).