Ezo (蝦夷) (also spelled Yezo or Yeso) is the Japanese term historically used to refer to the lands to the north of the Japanese island of Honshu. It included the northern Japanese island of Hokkaido, which changed its name from "Ezo" to "Hokkaidō" in 1869, and sometimes included Sakhalin and the Kuril Islands.
The same two kanji used to write the word "Ezo", which literally mean "shrimp barbarians" in Chinese, can also be read in the Japanese language as "Emishi", the name given to the indigenous people of these lands, the descendants of whom are most likely the Ainu people.
"Ezo" is a Japanese word meaning "foreigner" and referred to the Ainu lands to the north, which the Japanese named "Ezo-chi". The spelling "Yezo" reflects its pronunciation c. 1600, when Europeans first came in contact with Japan. It is this historical spelling that is reflected in the scientific Latin term yezoensis, as in Fragaria yezoensis and Porphyra yezoensis. However, there are species that use the new spelling such as the Japanese scallop known as hotategai (帆立貝): Mizuhopecten yessoensis.
The first published description of Ezo in the West was brought to Europe by Isaac Titsingh in 1796. His small library of Japanese books included Sangoku Tsūran Zusetsu (三国通覧図説, An Illustrated Description of Three Countries) by Hayashi Shihei. This book, which was published in Japan in 1785, described the Ezo region and its people.
In 1832, the Oriental Translation Fund of Great Britain and Ireland supported the posthumous abridged publication of Titsingh's French translation of Sankoku Tsūran Zusetsu. Julius Klaproth was the editor, completing the task which was left incomplete by the death of the book's initial editor, Jean-Pierre Abel-Rémusat.
Ezo (蝦夷) or Ezogashima (蝦夷ヶ島) (lit., "Island of the Ezo") was divided into several districts. The first was the "Wajinchi", or Japanese Lands, which covered the Japanese settlements on and around the Oshima Peninsula. The rest of Ezo was known as the Ezochi (蝦夷地) (lit., "Ezo-land"), or Ainu Lands. Ezochi was in turn divided into three sections: North Ezochi covered southern Sakhalin; West Ezochi included the northern half of Hokkaidō; and East Ezochi included the populous southern Hokkaidō and the Kuril Islands.
- Batchelor, John. (1902). Sea-Girt Yezo: Glimpses at Missionary Work in North Japan, pp. 2-8.
- Harrison, John A., "Notes on the discovery of Ezo", Annals of the Association of American Geographers Vol. 40, No. 3 (Sep., 1950), pp. 254-266 
- Nussbaum, Louis-Frédéric. (2005). "Ezo" in Japan Encyclopedia, p. 184.
- Editors: David N. Livingstone and Charles W. J. Withers (1999) "Geography and Enlightenment", University of Chicago Press, page 206 
- Haywood, John; Jotischky, Andrew; McGlynn, Sean (1998). Historical Atlas of the Medieval World, AD 600-1492. Barnes & Noble. pp. 3.24–. ISBN 978-0-7607-1976-3.
- WorldCat, Sangoku Tsūran Zusetsu; alternate romaji Sankoku Tsūran Zusetsu
- Cullen, Louis M. (2003). A History of Japan, 1582-1941: Internal and External Worlds, p. 137., p. 137, at Google Books
- Klaproth, Julius. (1832). San kokf tsou ran to sets, ou Aperçu général des trois royaumes, pp. 181-255., p. 181, at Google Books
- Frey, Christopher J. (2007) Ainu Schools and Education Policy in Nineteenth-century Hokkaido, Japan p.5, p. 5, at Google Books
- Cullen, Louis M. (2003). A History of Japan, 1582-1941: Internal and External Worlds. Cambridge: Cambridge University Press. ISBN 9780521821551; ISBN 9780521529181; OCLC 50694793
- Hayashi, Shihei. (1786). Sangoku Tsūran Zusetsu (三国通覧図説, An Illustrated Description of Three Countries). Edo: Manuscript. OCLC 44014900
- Klaproth, Julius. (1832). San kokf tsou ran to sets, ou Aperçu général des trois royaumes. Paris: Oriental Translation Fund of Great Britain and Ireland. OCLC 2563166; also OCLC 561284561