The "Book of Aneirin" is a thirteenth-century manuscript collection of Welsh praise-poetry. In comparison with other Welsh sources of similar date, the language of this text exhibits a number of features which have been interpreted as archaisms and taken as indications of great antiquity for the text. However, particularly in syntax, claims about the status of these 'archaisms' have not been discussed in the context of the grammatical organisation of the text as a whole. This book approaches various aspects of grammar against the background of a comprehensive edition of the finite verbal clauses of the text.