- Jackson, Kenneth Hurlstone. 1967. A Historical Phonology of Breton. Dublin: Dublin Institute of Advanced Studies.
- réimpression en 1986.
Fleuriot & Fleuriot (1977:16): "Making a masterful use of all the important material existing in Old and Middle Breton, he has laid the foundations for a general history of Breton. It is the most important book published so far on the history of this language. Arzel Even issued, in Breton, under the title Istor ar Yezhou Keltiek, a clear and useful manual giving the main features of all the Celtic languages. The first part is now outdated by Jackson's new book."