Domesday Book (also known as Domesday, or Book of Winchester), was the record of the great survey of England completed in 1086, executed for William the Conqueror, that was like a census by the government today. He needed information about the country he had just conquered so he could administer it. One of the main purposes of the survey was to find out who owned what so they could be taxed on it, and the judgment of the assessors was final -- whatever the book said about who owned the property, or what it was worth, was the law, and there was no appeal from it. Hence the name "Domesday" (Middle English spelling of "Doomsday") since the 12th century, which emphasizes the definitiveness and authority of the book, (the analogy refers to the Christian notion of a Last Judgement).