Junk is a type of ancient Chinese sailing ship that is still in use today. Junks were used as seagoing vessels as early as the 2nd century AD and developed rapidly during the Song Dynasty (960–1279). They evolved in the later dynasties, and were used throughout Asia for extensive ocean voyages. They were found, and in lesser numbers are still found, throughout South-East Asia and India, but primarily in China. Found more broadly today is a growing number of modern recreational junk-rigged sailboats.

The term junk may be used to cover many kinds of boat, ocean-going, cargo-carrying, pleasure boats, live-aboards. They vary greatly in size and there are significant regional variations in the type of rig, however they all employ fully battened sails.

Junks were efficient and sturdy ships that sailed long distances as early as the 2nd century AD, although whether this is indeed a date by which the hull form which we know as the junk's had found its final form is extremely dubious. Most scholars consider it was the early Song Dynasty (c.10th century CE) before the fully developed hull forms and rigs were in regular use in offshore trade. The fully developed junk design exhibited innovative, though subsequently very little further developed sail plans and hull designs.

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