Understanding Society, the UK Household Longitudinal Study, builds on the success of the British Household Panel Survey (BHPS). This paper describes some of the key elements of the design and conduct of the study and suggests how Understanding Society is distinctive as a longitudinal survey. Its large sample size offers new opportunities to study sub-groups that may be too small for separate analysis on other studies. The new content included in Understanding Society, not least the bio-measures, provides exciting prospects for interdisciplinary research across the social and medical sciences. The Innovation Panel is already proving to be an invaluable resource for research in longitudinal survey methodology. Finally, the inclusion of the BHPS sample within Understanding Society enables this long running panel to continue into the future, opening up inter-generational research and the opportunity to look at very long-term trajectories of change. This paper also describes the four sample components: the general population sample, ethnic minority boost sample, the Innovation Panel, and participants from the BHPS. Each component has a multistage sample designs, mostly with stratification and clustering. A complex weighting strategy is being developed to support varied analyses. This overview also describes the instruments, methods of data collection, and the timetable for data collection. A summary of the survey content’s is provided. With the data becoming available the user community is beginning to benefit from this investment in longitudinal studies.