The Book of Taliesin (Welsh: Llyfr Taliesin) is one of the most famous of Middle Welsh manuscripts, dating from the first half of the 14th century though many of the fifty-six poems it preserves are taken to originate in the 10th century. The manuscript, known as Peniarth MS 2 and kept at the National Library of Wales, is incomplete, having lost a number of its original leaves including the first. It was named Llyfr Taliessin in the 17th century by Edward Lhuyd and hence is known in English as "The Book of Taliesin".

The volume contains a collection of some of the oldest poems in Welsh, though many of them, particularly those attributed to the Dark Age poet Taliesin who was active towards the end of the 6th century, would have been composed in the Cumbric dialect of the north.

A core of praise poems of Urien Rheged is generally attributed to the historical Taliesin. The manuscript also preserves a few hymns, a small collection of elegies to famous men such as Cunedda and Dylan Eil Ton and also famous enigmatic poems such as The Battle of Trees and The Spoils of Annwfn (in which the poet claims to have sailed to another world with Arthur and his warriors). Several of these contain internal claims to be the work of Taliesin, but cannot be.