The monograph, for the first time in world practice, presents a comprehensive description of the ancient Welsh language. The first part examines questions about the place of the Old Welsh language in the history of Celtic languages, aspects of the manuscript tradition in early medieval Wales and analyzes the monuments of the Welsh language of this period; in the second, a grammatical outline of the ancient Welsh language is given. The last part of the book contains a selection of ancient Welsh texts, presenting selected glosses, poetic and prose fragments; the texts are accompanied by glossaries, and the most complex fragments are specially commented on. For specialists in Celticology, comparative historical linguistics and medieval studies, as well as for graduate and undergraduate students.