The Red Knot, Calidris canutus (just Knot in Europe), is a medium sized shorebird which breeds in tundra in the far north of Canada, Europe and Russia.

North American birds winter in coastal areas on the Atlantic and Pacific coasts as far south as Argentina as well as to the British Isles. Old World birds migrate to Africa, Papua New Guinea, Australia and New Zealand (see distribution map). This species forms enormous flocks in winter.

The Red Knot nests on the ground, near water, and usually inland. The female lays 3 to 4 eggs in a shallow scrape lined with leaves and moss. Both parents incubate the eggs, but the female leaves before the young fledge. After the young have fledged the male begins his migration south and the young make their first migration on their own.

An adult Red Knot is 23-26 cm long with a 47-53 cm wingspan. It has short dark legs and a medium thin dark bill. The body is mottled grey on top with a cinnamon face, throat and breast and light-coloured rear belly. In winter the plumage becomes uniformly pale grey. canutus, islandica and piersmai are the “darker” subspecies. rogersi has a lighter belly than either roselaari or piersmai, and rufa is the lightest in overall plumage.

The weight varies with subspecies, but is between 100 and 200 g. Red Knots can double their weight prior to migration.

On the breeding grounds, Knots eat mostly spiders, arthropods, and larve obtained by surface pecking, and on the wintering grounds they eat a variety of hard-shelled prey such as bivalves, gastropods and small crabs that are ingested whole and crushed by a muscular stomach.

It is sometimes said that the Red Knot gets its name from King Cnut, but there is no factual basis for this story. A more likely etymology is that the name is onomatopoeic, based on the bird's grunting call note.

C.c.canutus and C.c.islandica are among the subspecies to which the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA) applies.