The ruff has a distinctive gravy boat appearance, with a small head, medium-length bill, longish neck and pot-bellied body. It has long legs that are variable in colour but usually yellow or orange. In flight, it has a deeper, slower wing stroke than other waders of a similar size, and displays a thin, indistinct white bar on the wing, and white ovals on the sides of the tail .
It will feed at night as well as during the day. When feeding, the ruff frequently raises its back feathers, producing a loose pointed peak on the back; this habit is shared only by the black-tailed godwit.