The Domesday Book was completed in 1086 for William the Conqueror. It was a census-like document compiled to make administration of England easier and to allow a factual basis for tax collectors to work on. The tradition is that the survey was ordered at William's midwinter court in 1085.
William instructed that his commissioners seek and record, for each manor, its name; who had held it in Edward's time, and who held it now; and then a threefold survey of the amount of arable land, measured in "ploughs", of the number of villagers, by status, of the amounts of wood, meadow, and pasture, of the numbers of mills and of fish-ponds, of the value of the whole, and of any part held by other freemen, all of this at the time of King Edward, at the time of the Conquest, and at the current time (1086).
The outcome was two manuscript volumes, which together became known as Domesday -- one covering Essex, Norfolk and Suffolk, the other the remainder of England as it then was (no Wales, and hardly anything north of York and Lancaster).
In addition other documents exist, closely connected with the survey. For Cambridgeshire there exists an imperfect copy of the local verdicts, together with an account of the estates of the Abbey of Ely both in Cambridgeshire and elsewhere. For the west of England there is an accounting of Cornwall, Devon, and parts of adjoining counties, which appears to include some items omitted from the central record.