This chapter discusses the generation construct in relation to the cohort construct as structural, analytical categories in sociological studies of ageing. When studying aggregated categories, such as generations and cohorts, individual diversity and variations are toned down in favour of the collective characteristics. The chapter aims to clarify some of the distinctions between the various meanings of the cohort construct and the generation construct. The characteristics of family generations are quite distinct from those of generations as birth cohorts and generations as actualities. By combining analysis of age strata with analysis of cohorts, the age stratification perspective is thought to encompass both changes in life and changes in structures. When comparing the cohort constructs with the various generation constructs elaborated by Karl Mannheim, scholars can identify some similarities, but also some differences. One of the empirical implications of the theoretical constructs of cohort and generations is how they are to be operationalized and empirically determined.