The Domesday Book is the earliest public record in England (late 11th century) which detailed the lands and resources held by the King and his, heretofore, countless tenants.
    [note: the book was written in Latin - click on above image to view]

On Christmas Day in 1085, 20 years after the Norman Conquest of England, William the Conqueror ordered a complete survey of all the lands in England. He commissioned the great survey to discover the resources and taxable values of all the boroughs and manors in England. He wanted to document all citizens and list all their lands and possessions to discover who owned what, how much it was worth, and how much was owed to The King of England.
It was a massive enterprise, and the record of that survey, Domesday Book, was a remarkable achievement.
 

The Domesday Book was compiled during 1085/86 and remained as the only English census record until 1801. In addition to documenting land ownership, it was probably also used for the purpose of recording taxes and determining military service within the primitive feudal system. It has remained to this day as one of the most researched books in the world. The huge volumes recorded who owned the land, who lived on it, the types of livestock on the land, it's value, and the taxes which were due the monarchy. It was originally called the "King's Book" and then the "Great Book of Winchester" due to it's location, for centuries, at Winchester, the capital of the ancient Saxon Kingdom of Wessex. The book eventually became known as "Domesday" because the Anglo-Saxons, to whom it applied, felt it resembled God's final day of judgment. However, the book was held in reverence, as it has has always been to this day.  An Anglo Saxon landowner described the book in this way:
"He sent his men all over England into every shire ... Also he had a record made of ... how much everybody had who was occupying land in England, in land or cattle, and how much money it was worth. So very narrowly did he have it investigated, that there was no single hide nor a yard of land, nor indeed (it is a shame to relate but it seemed no shame to him to do) one ox nor one cow nor one pig which was there left out, and not put down in his record: and all these records were brought to him afterwards."

The Domesday Book was England's most complete and detailed survey until the modern census came along in the 19th century. The historic book is now housed at the Public Records Office in London. It is divided into two volumes - "Great Domesday" and "Little Domesday". "Great Domesday" has two parts and describes 31 counties. "Little Domesday" (which, ironically, is the larger of the 2 books) is bound in 3 parts and is devoted to the 3 largest English counties, Essex, Norfolk, and Suffolk. As is the case in even a modern day census, it was out of date before it's completion. Estate ownership, sub-tenants, buildings, and of course, livestock, changed hands during the 2 year survey.

An important feature of this ancient manuscript is the manner that names were recorded. Due to  the conquest and settlement of England's territories by the Normans ("Northmen"/"Norsemen"), descendents of the Vikings) many of the names entered were Norman influenced names. More importantly, for the first time known in history, the use of first and last names were recorded for the documented individuals and families. The names were often "Trade Names", William the Blacksmith {Smith}" - John the Tailor {Taylor}, etc. Others referred to locations - Steven of Eastwood, David of Essex, etc. Thus began the practice of family surnames which has had a revolutionary effect on all facets of historical and genealogic research and studies.

*  Author's Note:
 I've just discovered a new website that will explain much more, and especially should prove to be an extraordinary genealogic tool.
http://www.nationalarchives.gov.uk/documentsonline/domesday.asp