The Book of Llandaff (Latin: Liber Landavensis; Welsh: Llyfr Llandaf, Llyfr Llan Dâv, or Llyfr Teilo), is the chartulary of the cathedral of Llandaff, a 12th-century compilation of documents relating to the history of the diocese of Llandaff in Wales. It is written primarily in Latin but also contains a significant amount of Old and Middle Welsh names and marginalia.