The Book of Deer (Leabhar Dhèir in Gaelic) (Cambridge University Library, MS. Ii.6.32) is a 10th-century Latin Gospel Book with early 12th-century additions in Latin, Old Irish and Scottish Gaelic. It is noted for containing the earliest surviving Gaelic writing from Scotland.
The origin of the book is uncertain, however it is reasonable to assume that the manuscript was at Deer, Aberdeenshire, Scotland when the marginalia were written. It may be the oldest surviving manuscript produced in Scotland, and is notable for having possibly originated in what is now considered a Lowland area. The manuscript belongs to a category of what are known today as Irish pocket Gospel Books, which were produced for private rather than for liturgical use. While the manuscripts to which the Book of Deer is closest in character are all Irish, most scholars argue for a Scottish origin. The book has 86 folios and measures 54 mm by 107 mm. It is written on vellum in brown ink and is in a modern binding.