This paper discusses the design decisions made in the incorporation of the British Household Panel Survey (BHPS), a long-running household panel survey in the UK, into a new and larger study,  Understanding Society: the UK Household Longitudinal Study.  The paper sets out the background to the new study, the key features of the new study and its potential for analysis, the survey design of Understanding Society and the decisions made in incorporating the BHPS sample into the new design, and the decisions around continuity and innovation in the content of the questionnaires.