(July 29, 1858), agreement that secured commercial and diplomatic privileges for the United States in Japan and constituted the basis for Western economic penetration of Japan. Negotiated by Townsend Harris, first U.S. consul to Japan, it provided for the opening of five ports to U.S. trade, in addition to those opened in 1854 as a result of the Treaty of Kanagawa; it also exempted U.S. citizens living in the ports from the jurisdiction of Japanese law, guaranteed them religious freedom, and arranged for diplomatic representation and a tariff agreement between the United States and Japan.

Harris was aided by the fact that British and French squadrons were on their way to Japan to obtain new treaties by force; he persuaded the Japanese authorities that they would obtain better terms by first negotiating a new treaty with the United States. And, indeed, the Harris Treaty became the basis of agreements signed shortly afterward with most European nations. Although the treaty provided for the possibility of revision in 1872, the Iwakura Mission to the United States that year failed to secure modification of the agreements.