The early-twelfth-century Book of Llandaf is rightly notorious for its bogus documents - but it also provides valuable information on the early medieval history of south-east Wales and the adjacent parts of England. This study focuses on its 159 charters, which purport to date from the fifth century to the eleventh, arguing that most of them are genuine seventh-century and later documents that were adapted and "improved" to impress Rome and Canterbury...