The Sound Structure of Modern Irish contains a comprehensive description of the phonology of Irish. Based on the main forms of the language, it offers an analysis of the segments and the processes in its sound system. Each section begins with a description of the area of phonology which is the subject - such as stress patterns, phonotactics, epenthesis or metathesis - and then proceeds to consider the special aspects of this subject from a theoretical and typological perspective.

The book pays particular attention to key processes in the sound system of modern Irish. The two most important of these are palatalisation and initial mutation, phenomena which are central to Irish and the analysis of which has consequences for general phonological theory.

The other main emphasis in the book is on a typological comparison of several different languages, all of which show palatalisation and/or initial mutation as part of their systems. The different forms of Celtic, Slavic languages, Romance dialects and languages along with languages such as Finnish, Fula, Nivkh and Southern Paiute are considered to find out how processes which are phonetic in origin (external sandhi) can become functionalised and integrated into the morphosyntactic system of a language.