The Treaty of Nanking (or Nanjing) was signed on 29 August 1842 to mark the end of the First Opium War (1839–42) between the United Kingdom of Great Britain and Ireland and the Qing Dynasty of China. It was the first of what the Chinese called the unequal treaties because Britain had no obligations in return.

In the wake of China's military defeat, with British warships poised to attack the city, representatives from the British and Qing Empires negotiated aboard HMS Cornwallis anchored at Nanking. On 29 August 1842, British representative Sir Henry Pottinger and Qing representatives, Qiying, Yilibu, and Niujian, signed the treaty. It consisted of thirteen articles and ratification by Queen Victoria and the Daoguang Emperor was exchanged nine months later.

The fundamental purpose of the treaty was to change the framework of foreign trade which had been in force since 1760 (Canton System). The treaty abolished the monopoly of the Thirteen Factories on foreign trade (Article V) in Canton and instead five ports were opened for trade, Canton (Shameen Island until 1943), Amoy (Xiamen until 1930), Foochowfoo (Fuzhou), Ningpo (Ningbo) and Shanghai (until 1943), where Britons were to be allowed to trade with anyone they wished. Britain also gained the right to send consuls to the treaty ports, which were given the right to communicate directly with local Chinese officials (Article II). The treaty stipulated that trade in the treaty ports should be subject to fixed tariffs, which were to be agreed upon between the British and the Qing governments (Article X).