The Book of Deer is thought to have been made in a Columban manastery at Old Deer in Aberdeenshire, Scotland, in around 1150. This book of visual realisations of individual masterpieces of Celtic illuminated art is the first in a series.
I picked this book up for two reasons: it happened to appear on a list of low use material at the university library where I work, and round about the same time I saw a tweet from a Scot suggesting that the Book of Deer should be returned to Scotland (it is held at Cambridge University Library). I borrowed the book, partly to inform myself a bit better about the Book of Deer (which may I suppose appear in the news at some point if there is a movement for its repatriation), and to see why it hadn't been borrowed recently by anyone else.
This is not a heavy academic work. It contains a good factual, readable summary of the history of the Book of Deer, which is an incomplete but substantial section of an illuminated gospel thought to date from the ninth century, created at the original monastery of Deer near Aberdeen. It was probably plundered from Scotland and eventually came into the hands of George I, who gave it to Cambridge. It contains illustrations including what are described as "pagan Celtic" motifs, and it also contains marginalia in Scottish Gaelic, which show the development of the language at a time of transition (from Old Irish). The book is "no. 1" in a series, "Library of Celtic illuminated manuscripts", but there seem not to have been any more. The introduction is by Peter Berresford Ellis, a well-known writer on "Celtic" subjects. A large part of the book consists of Roy Ellsworth's copies of the artwork of the manuscript (so no actual reproductions). You would have to look elsewhere for a detailed discussion of the linguistic significance (the introduction summarises the history of the study of this aspect and refers to the published works on it): this book is really about the art. It's a good introduction, and I am keeping it in the library but giving it a bit of help with a more detailed catalogue record and moving it to a different section, in the hope that it might be more "findable".