This book is concerned with the structure and status of the Celtic languages. At fi rst glance this may appear to give the work a very defi nite focus. However, the question of what constitutes a ‘Celtic’ language is not as straightforward as linguists may suppose. This is because there are at least three different approaches to defi ning what is meant by such terms as ‘Celtic’, ‘Romance’ or ‘Slavic’. Historically all three approaches have been applied to the Celtic languages, each successive view further refi ning and narrowing the scope of enquiry. These are: an ethnological approach; a genetic approach; and a typological approach.