Tonkin refers to:

Vietnam

• Đông Kinh, a former name of Hanoi, Vietnam
• Tonkin, an exonym for northern Vietnam
• the French protectorate of Tonkin, the northern part of French Indochina
• Gulf of Tonkin, a gulf in the South China Sea
• Gulf of Tonkin incident, a 1964 naval incident that precipitated the Gulf of Tonkin Resolution
• Gulf of Tonkin Resolution, the 1964 resolution of the US Congress that precipitated the buildup of US forces in Vietnam
• In France, the Sino-French War (1884–1885) is termed the Tonkin War.
• the Tonkin Affair, a political crisis in France

People

• Anthony Tonkin (b. 1980), English footballer
• Arthur Tonkin (politician) (1930–2022), Australian politician
• Arthur Tonkin (rugby union) (1922–1991), Australian rugby player
• David Tonkin (1929–2000), Premier of South Australia
• Felicity Tonkin (b. 1985), daughter of Mark Phillips and Heather Tonkin
• Humphrey Tonkin (b. 1939), American-British professor and Esperantist
• John Tonkin (1902–1995), Premier of Western Australia
• Michael Tonkin (b. 1989), American professional baseball player
• Phoebe Tonkin (b. 1989), Australian actress

Other

• Tonkin Highway, a major arterial road in Perth, Western Australia
• Tonkin Railway in Switzerland
• Tonkin Street in Hong Kong
• Tonkinese cat, cat breed
• A type of Bamboo (Arundinaria amabilis or Pseudosasa amabilis).
• Tokyo