Theoretical positions which argue for age-related and individual variation in profiles of psychological functioning and patterns of predictive relationships are reviewed in the context of the three domains investigated by the Psychology Unit of the Berlin Aging Study (BASE): intelligence and cognition, self and personality, and social relationships. To illustrate the potential of BASE, we report initial data for a small set of variables from these three psychological domains for the first wave of study participants (N = 360, age range 70 to 103 years). Our analyses of these data were targeted toward three key questions about differential psychological ageing: namely, the extent of age/cohort-related differences and individual variation within each domain, possible age differences in the structural relationships between the three domains, and subgroup variations in cross-domain profiles of functioning. Within domains, individual differences in general were very large. Chronological age accounted for a sizeable proportion of the variance only in the domain of cognitive performance. The structural relationships between the domains of psychological functioning were similar for the old and very old age groups and reflected much domain independence. Examination of subgroup variations in cross-domain profiles of functioning revealed ten subgroups. All subgroups showed an uneven, that is, age-selective group membership: five subgroups included more of the very old, two more of the old, and three were age-specific. Preliminary explorations of these subgroups suggested substantial links to selected health-related variables, supporting proposals for multi-disciplinary research into differential ageing.