The willet (Tringa semipalmata) is a large shorebird in the family Scolopacidae. It is a relatively large and robust sandpiper and is the largest of the species called "shanks" in the genus Tringa. Its closest relative is the lesser yellowlegs, a much smaller bird with a very different appearance apart from the fine, clear, and dense pattern of the neck, which both species show in breeding plumage. It breeds in North America and the West Indies and winters in southern North America, Central America, the West Indies and South America.

The willet was formally described in 1789 by the German naturalist Johann Friedrich Gmelin in his revised and expanded edition of Carl Linnaeus's Systema Naturae. He placed it in the genus Scolopax and coined the binomial name Scolopax semipalmata. Gmelin based his description on the "semipalmated snipe" from New York that had been described in 1785 by both the English ornithologist John Latham and by the Welsh naturalist Thomas Pennant. The willet was formerly assigned to the genus Catoptrosorus that had been introduced for the species in 1827 by Charles Lucien Bonaparte. In 2006 it was moved to the current genus Tringa based on a molecular phylogenetic study published the previous year. The genus name Tringa is the Neo-Latin word given to the green sandpiper by the Italian naturalist Ulisse Aldrovandi in 1603 based on Ancient Greek trungas, a thrush-sized, white-rumped, tail-bobbing wading bird mentioned by Aristotle. The specific epithet semipalmata combines the Latin semi- meaning "half" or "small" with palmatus meaning "palmate".

Two subspecies are recognised:

It has been suggested that the two subspecies be treated as separate species as there are clear differences in distribution, behavior, morphology, and genetics, but this has yet to be widely adopted.

The willet is a very rare vagrant to Europe with records from the Azores, mainland Portugal, France, Norway and Finland. The Portuguese record from Alcochete near Lisbon on 29 April 2009 showed characteristics of the eastern subspecies.

The willet is an inelegant and heavily built shorebird with a structure similar to that of the common redshank but being larger in size than the greater yellowlegs while resembling a godwit in flight with black primary coverts and primaries contrasting with a broad white band, white secondaries with a white rump and gray tail band. With its reclassification into the Tringa genus, it stands as the largest species in this prominent sandpiper genus. It is 31–41 cm (12–16 in) in overall length and weighs 200–330 g (7.1–11.6 oz). The sexes are similar in plumage but the female is slightly larger.

The black underwing coverts may be conspicuous in flight. Willets are identified on the ground by their gray legs and shortish, heavy but straight bill. The plumage is gray above with a white rump, and white below with a distinct white area above the lores and a narrow whitish eye ring giving the bird a spectacled appearance. The underparts are white. In breeding plumage, the bird shows brown barring on the upperparts. Non-breeding birds are plainer.^{[citation needed]}

The willet's name is onomatopoeic and refers to its loud piercing "pill-will-willet" territorial song., which is higher pitched and repeated at a faster rate in Eastern willets than in Western birds. Other calls include a predator response call given by breeding birds which is a repeated, staccato "kleep", while non breeding birds alarms include a high, pitched anxious "kip-kip-viek" call and a "kreei" call. They also have a distinctive call when crossing another willet's territory and this "klay-dir" call is also used as a contact call when willets are migrating.