Peter Duck is the third book in the Swallows and Amazons series by Arthur Ransome. The Swallows and Amazons sail to Crab Island with Captain Flint and Peter Duck, an old sailor, to recover buried treasure. During the voyage the Wildcat (Captain Flint's ship) is chased by another vessel, the Viper, whose piratical crew are also intending to recover the treasure.

The book, first published in 1932, is considered to be one of the metafictional books in the series, along with Missee Lee. It is a story withing the stories of The Swallows and Amazons. Most of the book was written in Aleppo where Ransome was staying with the Altounyans.