The exact extent of the Irish literature still remaining in manuscript has never been adequately determined. M. d'Arbois de Jubainville has noted 133 still existing manuscripts, all copied before the year 1600, and the whole number which he has found existing chiefly in public libraries on the Continent and in the British Isles amounts to 1,009. But many others have since been discovered, and great numbers must be scattered throughout the country in private libraries, and numbers more are perishing or have recently perished of neglect since the "National Schools" were established. Jubainville quotes a German as estimating that the literature produced by the Irish before the seventeenth century, and still existing, would fill a thousand octavo volumes. It is hard to say, however, how much of this could be called literature in a true sense of the word, since law, medicine, and science were probably included in the calculation. O'Curry, O'Longan, and O'Beirne Crowe catalogued something more than half the manuscripts in the Royal Irish Academy, and the catalogue of contents filled thirteen volumes containing 3,448 pages. To these an alphabetic index of the pieces contained was made in three volumes, and an index of the principal names, etc., in thirteen volumes more. From a rough calculation, based on an examination of these, I should place the number of different pieces catalogued by them at about ten thousand, ranging from single quatrains or even single sentences to long poems and epic sagas. But in the Academy alone, there are nearly as many more manuscripts which still remain uncatalogued.
It is probably owing to the extreme difficulty of arriving at any certain conclusions as to the real extent of Irish literature that no attempt at a consecutive history of it has ever previously been made. Despite this difficulty, there is no doubt that such a work would long ago have been attempted had it not been for the complete breakdown and destruction of Irish Ireland which followed the Great Famine, and the unexpected turn given to Anglo-Irish literature by the efforts of the Young Ireland School to compete with the English in their own style, their own language, and their own models.