This grammar is the most comprehensive treatment of any variety of Irish Gaelic. It is the fruit of over twenty years of collaboration with speakers from west Connacht (Iorras Aithneach, County Galway). It is based on extensive field-work, published and unpublished lore, and recent as well as older recordings. These sources provide a picture of widespread variation and change across the six generations born between 1850 and 2000. The grammar draws on several branches of linguistics: descriptive and historical linguistics, dialectology and sociolinguistics.

Many topics previously untouched in Irish linguistics are dealt with in considerable detail. For instance, a definitive analysis of phonemic nasalisation as well as the step-by-step intergenerational loss of such nasalisation and its interaction with nasal speech setting; a complex shift in place of articulation of coronal consonants and one vowel; family-specific morphological use; instances of dialect mixture through the influence of parents on their children; innovative pronominal use conditioned, among other features, by the sex of speakers; explanation of innovative genitive and plural suffixes; combinatorial possibilities of prefixes; variables with a wide range of variants, termed hypervariables, and the licensing of such heterogeneity; the grammar of higher register in folklore; change in 'young people’s dialect' including simplification and loss of distinctions.

Volume I provides an introduction and chapters on historical phonology, sandhi and nominal morphology.

Volume II describes plural noun morphology, the verb and pronominals.

Volume III contains chapters on prepositions, functors, initial mutations, higher register, borrowings and language contact, and onomastics.

Volume IV presents transcriptions and a CD containing recordings of a selection of speakers across the generations. The final volume also contains a vocabulary, bibliography and four indexes.