This book offers, for the first time, a complete collection of the textual documents known so far in the Old Welsh language. Dr. Alexander I. Falileyev’s edition of these documents is ac-companied by a running linguistic commentary as well as a glossary. The grammatical section of the book orders all the linguistic evidence found in these texts in a systematic form. Both, the textual evidence and the linguistic analysis allow a complete picture of the present state of the research on the Old Welsh language. Dr. Falileyev’s book originally appeared in Moscow in 2002 (Древневаллийский язык (Drevnevalliskiy yazyk)). It was updated by the author in 2007 and translated by Prof. Yves Le Berre (Brest) into French, so as to make this important work accessible to scholars not versed in the Russian language. The Old Welsh language is not only important for a wider understanding of the evidence of the other medieval Insular Celtic languages (Irish, Breton and Cornish), but also for the his-tory of English, as Old Welsh was the first language that speakers of nascent English were in contact with.