The manuscript which eventually came to be called "Domesday Book" is a product of the enterprise originally known as the "Descriptio totius Angliae", the survey carried out in 1086, twenty years after the Norman Conquest, by order of King William I. This manuscript does not stand alone. It is the latest of four successive versions of the written record of the survey. Intrinsically the least valuable, it has gained in value over time, as the earlier versions have dropped out of existence. But they have not disappeared completely. Part of the immediately preceding version survives as the companion volume to "Domesday Book"; part of the version preceding that survives, for some unknown reason, in the library of Exeter Cathedral, even though it was, without any doubt, written in the king's treasury at Winchester. The earliest version of all - the only version in which the data were recorded cadastrally, county by county, hundred by hundred, village by village, manor by manor - has been entirely lost in the original; yet for most of one county a copy survives, in a late twelfth-century manuscript from Ely. This book begins with a sequence of chapters which analyse some aspects of the manuscript evidence, from a new angle, or in closer detail than before, working backwards from the latest version towards the earliest. The last two chapters reassemble the evidence to create a new picture of the conduct of the survey, in both its fieldwork and its post-fieldwork phases.