Ezo (蝦夷, also spelled Yezo or Yeso) is a Japanese name which historically referred 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 Hokkaido in 1869, and sometimes included Sakhalin and the Kuril Islands. The word "Ezo" can also refer to the peoples that the Japanese encountered in these lands, referred to in modern times as 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 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 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 called the Ezochi, or Ainu Lands. Ezochi was in turn divided into three sections: North Ezochi covered southern Sakhalin; West Ezochi included the northern half of Hokkaido; and East Ezochi included the populous southern Hokkaido and the Kuril Islands.