The present and future of our society are characterized by an increasing proportion of older and very old people. The Berlin Aging Study (BASE) is unique worldwide in the breadth of the spectrum of involved sciences and the research areas defined both disciplinarily and interdisciplinarily, focusing on advanced age (70 to over 100 years) and empirically based on a representatively selected urban population. The volume reports on various topics, including cognitive performance, personality, and social relationships in old age, physical health, medical care, and dental status, mental illnesses such as dementia and depression, social and cultural activities, and economic situations, as well as daily competencies, subjective well-being, and differences between women and men. Since 20 years have passed since the initial surveys, during which the original study participants were interviewed up to seven additional times, the earlier results are supplemented by two chapters on the longitudinal continuation of the Berlin Aging Study. The longitudinal BASE dataset has proven to be a very fruitful field for diverse analyses of the aging process, inter- and intra-individual differences in aging, and the causal relationships between functional areas. The study was originally conducted as part of the working group 'Aging and Social Development' of the Berlin-Brandenburg Academy of Sciences. The authors from various disciplines have predominantly worked at the Max Planck Institute for Human Development, the Free University of Berlin, and Humboldt University of Berlin, with some now conducting research in the field of gerontology abroad.