Tonkin, also spelled Tongkin, Tonquin or Tongking, is an exonym referring to the northern region of Vietnam. During the 17th and 18th centuries, this term referred to the domain Đàng Ngoài under Trịnh lords' control, including both the Northern and Thanh-Nghệ regions, north of the Gianh River. From 1884 to early 1945, this term was used for the French protectorate of Tonkin, composed of only the Northern region.

Vietnam, officially the Socialist Republic of Vietnam (SRV), is a country at the eastern edge of mainland Southeast Asia, with an area of about 331,000 square kilometres (128,000 sq mi) and a population of over 100 million, making it the world's fifteenth-most populous country. Vietnam shares land borders with China to the north, and Laos and Cambodia to the west. It shares maritime borders with Thailand through the Gulf of Thailand, and the Philippines, Indonesia, and Malaysia through the South China Sea. Its capital is Hanoi and its largest city is Ho Chi Minh City.