The Hăijìn or sea ban was a series of related isolationist policies restricting private maritime trading and coastal settlement during most of the Ming Empire and early Qing Empire. Despite official proclamations the Ming policy was not enforced in practice, and trade continued without hindrance. The early Qing dynasty's anti-insurgent "Great Clearance" was more definitive with devastating effects on communities along the coast.

First imposed to deal with Japanese piracy amid the mopping up of Yuan partisans, the sea ban was completely counterproductive: by the 16th century, piracy and smuggling were endemic and mostly consisted of Chinese who had been dispossessed by the policy. China's foreign trade was limited to irregular and expensive tribute missions, and the military pressure from the Mongols after the disastrous Battle of Tumu led to the scrapping of Zheng He's fleets. Piracy dropped to negligible levels only upon the end of the policy in 1567, but a modified form was subsequently adopted by the Qing. This produced the Canton System of the Thirteen Factories, but also the opium smuggling that led to First and Second Opium Wars in the 19th century.

The Chinese policy was mimicked in Edo period Japan by the Tokugawa shogunate, where the policy was known as kaikin (海禁)/Sakoku (鎖国); it was also mimicked by Joseon Korea, which became known as the "Hermit Kingdom", before they were opened militarily in 1853 and 1876.