Geoffrey of Monmouth's pseudohistorical History of the Kings of Britain (c. 1138) became one of medieval Europe's most popular and successful creations. Here, Jaakko Tahkokallio explores its high-medieval reception through a detailed examination of its extensive manuscript corpus. Geoffrey's pseudohistorical text introduced King Arthur and the prophet Merlin to European literature. Previous research has often portrayed Geoffrey's work as a radical departure from mainstream Latin historiography and emphasised its connections to emerging vernacular courtly literature. The evidence scrutinised in this book - the manuscripts' production histories, material characteristics, and marginalia - presents a challenge to this received wisdom, indicating instead that Geoffrey's History largely corresponded to, rather than challenged, the expectations of its medieval readers for historical texts. In its combination of fabulous and controversial content with the traditional form of Latin historical writing, it appealed to an extraordinary range of contemporary readers.