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 or before.

The volume contains some of the oldest poems in Welsh, possibly but not certainly dating back to the sixth century and to a real poet called Taliesin.

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 seventeenth century by Edward Lhuyd and hence is known in English as "The Book of Taliesin". The palaeographer John Gwenogvryn Evans dated the Book of Taliesin to around 1275, but Daniel Huws dated it to the first quarter of the fourteenth century, and the fourteenth-century dating is generally accepted.

The Book of Taliesin was one of the collection of manuscripts amassed at the mansion of Hengwrt, near Dolgellau, Gwynedd, by the Welsh antiquary Robert Vaughan (c. 1592–1667); the collection was eventually donated by Sir John Williams in 1907 to the newly established National Library of Wales as the Peniarth or Hengwrt-Peniarth Manuscripts.

It appears that some "marks", presumably awarded for poems, measuring their "value", are extant in the margin of the Book of Taliesin.

Titles adapted from Skene.

Many of the poems have been dated to the twelfth and thirteenth centuries and are likely to be the work of poets adopting the Taliesin persona for the purposes of writing about awen (poetic inspiration), characterised by material such as:

A few are attributed internally to other poets. A full discussion of the provenance of each poem is included in the definitive editions of the book's contents poems by Marged Haycock.^{[page needed][page needed]}