data for the book stems from recordings of more than 200 speakers and all the statements made about the structure of Irish are based on native speakers' speech samples. These are supplied online with a software interface which allows users to quickly orient themselves among the varieties of Irish via clickable maps. A number of further issues are focused on in the book, such as the possibility of dialect reconstruction and the use of place- name evidence for determining the earlier distribution of Irish. Additional historical and background information is provided so that scholars and students without any previous knowledge of the language can readily grasp the themes and issues discussed.