A junk (Chinese: 船, chuán) is a type of Chinese sailing ship with fully battened sails. There are two types of junk in China: northern junk, which developed from Chinese river boats,^: 20 and southern junk, which developed from Austronesian ships visiting southern Chinese coasts since the 3rd century CE. They continued to evolve in later dynasties and were predominantly used by Chinese traders throughout Southeast Asia. Similar junk sails were also adopted by other East Asian countries, most notably Japan where junks were used as merchant ships to trade goods with China and Southeast Asia. They were found, and in lesser numbers are still found, throughout Southeast Asia and India, but primarily in China. Historically, a Chinese junk could be one of many types of small coastal or river ships, usually serving as a cargo ship, pleasure boat, or houseboat, but also ranging in size up to large ocean-going vessel. Found more broadly today is a growing number of modern recreational junk-rigged sailboats. There can be significant regional variations in the type of rig or the layout of the vessel; however, they all employ fully battened sails.

The term "junk" (Portuguese junco; Dutch jonk; and Spanish junco) was also used in the colonial period to refer to any medium- to large-sized ships of the Austronesian cultures in Island Southeast Asia, with or without the junk rig. Examples include the Indonesian and Malaysian jong, the Philippine karakoa and lanong, and the Maluku kora kora.