The present and future of our society are shaped by an ever-increasing proportion of old and very old people. The Berlin Aging Study is one of the largest interdisciplinary efforts to explore old age and aging. Unique aspects of the Berlin Aging Study are the spectrum of scientific disciplines involved, the range of discipline-specific and interdisciplinary research topics, the focus on very old age (70 to over 100 years), and the empirical reference to a representative heterogenous urban population. The study's first cross-sectional findings on intellectual abilities, self and personality, social relationships, physical health, functional capacity, medical treatment, mental disorders such as depression and dementia, socioeconomic conditions, activities, everyday competence, subjective well-being, and gender differences are reported in depth in this book. The study was carried out in the context of the Berlin-Brandenburg Academy of Sciences study group on 'Aging and Social Development'. The authors primarily conduct their research at the Berlin Max Planck Institute for Human Development, the Free University of Berlin, and the Humboldt University, Berlin.