The Longitudinal Study (LS) contains records on more than 500,000 people usually resident in England and Wales at each point in time and is largely representative of the population. The LS is the largest longitudinal data resource in England and Wales. The LS has linked records at each census since the 1971 Census for people born on one of four selected dates in a calendar year. These four dates were used to update the sample at the 1981, 1991, 2001 and 2011 Censuses. Life events data are also linked for LS members, including births to sample mothers, deaths, and widow(er)hoods. New LS members enter the study through birth and immigration (if they are born on one of the four selected birth dates). They leave the study through death or emigration, although their data are retained for analysis. Data on approximately 1.2 million sample members has been collected over the 40 years of the study. The LS can be used for several types of analysis, over many different research areas. The studies that make best use of LS data are those that link social, occupational, and demographic information to data on life events. Examples include studies of mortality, cancer incidence and survival, and fertility patterns. The individual-level data of the LS means that person-years at risk can be calculated for epidemiological studies. The ability to combine detailed personal characteristics with area characteristics has proved useful in many studies of health, for example, those looking at environmental effects on health, and those on inequalities in health. Linked census data for members of the LS allow researchers to examine change between censuses by investigating the same people through two or more censuses. Studies of social mobility have examined changing class position by age. Information on co-residents of LS sample members has been used to study intergenerational mobility. The size of the LS makes it suitable for the study of ageing. Studies have used the information collected on the co-residents and family status of LS sample members to examine changes to household and family arrangements that come with age. Census forms ask about address one year ago. The linked census data in the LS have been used to study 10-year migration patterns between censuses. In addition, information on place of enumeration in 1939 has been used to study migration over longer periods. More detailed information about the LS and how to make use of it can be found on the ONS website link in Associated Media. A free user support service for UK-based researchers from the academic, public and voluntary sectors is provided by the Centre for Longitudinal Study Information & User Support (CeLSIUS) based at University College London. More information is provided at the UCL CeLSIUS website link in Associated Media.