The oldest books of miscellaneous literature are the Lebor na hUidre, or "Book of the Dun Cow", transcribed about 1100, and the Book of Leinster, which dates from about fifty years later. These books are great miscellaneous literary collections. After them come many valuable vellums. The date at which these manuscripts were penned is no criterion of the date at which their contents were first written, for many of them contain literature which, from the ancient forms of words and …

The earliest written form of the Irish language is known to linguists as Primitive Irish. Primitive Irish is known only from fragments, mostly personal names, inscribed on stone in the Ogham alphabet. The earliest of such inscriptions probably date from the 3rd or 4th century. Ogham inscriptions are found primarily in the south of Ireland as well as in Wales, Devon and Cornwall, where it was brought by settlers from Ireland to sub-Roman Britain, and in the Isle of Man.