the study of past patterns of population structure, FERTILITY, etc., using historical source material, especially for those periods prior to the first Census in 1801. In the UK, the subject has flourished particularly since the 1950s using data gathered from PARISH REGISTERS, wills, tombstones, and the like. The findings of this research (e.g. Laslett, 1972; Wrigley, 1966) have lead to a reappraisal of previous assumptions about the ‘preindustrial family’ (e.g. its ‘extended’ form). In more general terms, historical demography has thrown new light on the overall relation between family size and structure, patterns of sexual behaviour, social mobility and population change where data had been previously lacking. See also DEMOGRAPHY.