The book consists of three indexes. The Location Index lists Irish surnames in alphabetical order (disregarding the Mac or O' prefix) followed by code letters for the 10 sources in which the name was found and the location or line of descent (usually just the county) as given in the source cited. The Surname Index uses the same arrangement, but the code letters refer to 18 different sources (journals, monographs, and special reports), all of which are available from the publisher.