The 21 censuses that have been conducted in Britain since 1801, have provided an invaluable insight into Britain's social, political and economic history over the past 200 years. From their original purpose to assess how many men were fit for military duty in the Napoleonic wars, to being a necessary tool for determining government policy, the 10-yearly census return is a fascinating snapshot of the state of the population on a particular moment in each decade. The growth of Britain's cities; the movement of population away from the countryside; the variety of people's occupations; their way of life; and what religious beliefs they hold are all contained within the census reports. With the imminent publication of the 1921 census results, this will prove a useful introduction, both for those interested in general trends in social history, and those researching family history.