A sea shanty, shanty, chantey, or chanty (/ˈʃæntiː/) is a genre of traditional folk song that was once commonly sung as a work song to accompany rhythmical labor aboard large merchant sailing vessels. The term shanty most accurately refers to a specific style of work song belonging to this historical repertoire. However, in recent, popular usage, the scope of its definition is sometimes expanded to admit a wider range of repertoire and characteristics, or to refer to a "maritime work song" in general.

From Latin cantare via French chanter, the word shanty emerged in the mid-19th century in reference to an appreciably distinct genre of work song, developed especially on merchant vessels, that had come to prominence in the decades prior to the American Civil War. Shanty songs functioned to synchronize and thereby optimize labor, in what had then become larger vessels having smaller crews and operating on stricter schedules. The practice of singing shanties eventually became ubiquitous internationally and throughout the era of wind-driven packet and clipper ships.

Shanties had antecedents in the working chants of British and other national maritime traditions, such as those sung while manually loading vessels with cotton in ports of the southern United States. Shanty repertoire borrowed from the contemporary popular music enjoyed by sailors, including minstrel music, popular marches, and land-based folk songs, which were then adapted to suit musical forms matching the various labor tasks required to operate a sailing ship. Such tasks, which usually required a coordinated group effort in either a pulling or pushing action, included weighing anchor and setting sail.

The shanty genre was typified by flexible lyrical forms, which in practice provided for much improvisation and the ability to lengthen or shorten a song to match the circumstances. Its hallmark was call and response, performed between a soloist and the rest of the workers in chorus. The leader, called the shantyman, was appreciated for his piquant language, lyrical wit, and strong voice. Shanties were sung without instrumental accompaniment and, historically speaking, they were only sung in work-based rather than entertainment-oriented contexts. Although most prominent in English, shanties have been created in or translated into other European languages.

The switch to steam-powered ships and the use of machines for shipboard tasks by the end of the 19th century meant that shanties gradually ceased to serve a practical function. Their use as work songs became negligible in the first half of the 20th century. Information about shanties was preserved by veteran sailors and folklorist song-collectors, and their written and audio-recorded work provided resources that would later support a revival in singing shanties as a land-based leisure activity. Commercial musical recordings, popular literature, and other media, especially since the 1920s, have inspired interest in shanties among non-sailors. Contemporary performances of these songs range from the "traditional" style of maritime music to various modern music genres.

The origin of the word "shanty" is unknown, though several inconclusive theories have been put forth. One of the earliest and most consistently offered derivations is from the French chanter, "to sing".

The phenomenon of using songs or chants, in some form, to accompany sea labor preceded the emergence of the term "shanty" in the historical record of the mid-19th century. One of the earliest published uses of this term for such a song came in G. E. Clark's Seven Years of a Sailor's Life, 1867. Narrating a voyage in a clipper ship from Bombay to New York City in the early 1860s, Clark wrote, "The anchor came to the bow with the chanty of 'Oh, Riley, Oh,' and 'Carry me Long,' and the tug walked us toward the wharf at Brooklyn." While telling of another voyage out of Provincetown, Mass. in 1865, he wrote:

Every man sprang to duty. The cheerful chanty was roared out, and heard above the howl of the gale. The cable held very hard, and when it surged over, the windlass sent the men flying about the deck, as if a galvanic battery had been applied to their hands. The vessel's head was often buried in the solid seas, and the men, soaked and sweating, yelled out hoarsely, "Paddy on the Railway", and "We're Homeward Bound", while they tugged at the brakes, and wound the long, hard cable in, inch by inch.