The Treaty of Amity and Commerce was an agreement signed in 1858 between the United States and the Kingdom of Siam, now known as Thailand. This treaty aimed to establish friendly relations and promote trade between the two nations, allowing American merchants to operate in Siam and vice versa. The treaty included provisions for the protection of citizens, the establishment of consulates, and the regulation of trade tariffs. It marked a significant step in U.S. foreign relations in Asia, reflecting a growing interest in expanding commercial ties in the region during the 19th century.