The present »Etymological Glossary of Old Welsh« is intended to offer an alphabetically arranged list of words which are found in the manuscripts transcribed before the beginning of the Middle Welsh period, and to provide them with the most important published references. Only the records written down during the Old Welsh period have been used is the compilation of the glossary. The only text which was not used is the »Book of Llan Dav«, which still requires to be comprehensively discussed, and is a subject for research on its own right. The focus has been laid on the collection of the published analysis of the rudiments of Old Welsh; thus the glossary could be viewed as an extended bibliography for Old Welsh studies.