The educational development and achievements of children depend on individual prerequisites as well as on familial and institutional learning contexts. Data from the study BiKS-3-18 (Educational Processes, Competence Development, and Formation of Educational Decisions in Preschool and School Age) enables educational research on mechanisms and long-term effects of early child development and different learning environments in Germany. This contribution provides an overview of the study design, sampling procedures and sizes, contents, and research potential of the BiKS-3-18 study. Starting in 2005, the study followed preschool children from Bavaria and Hesse from the age of three over fifteen years, from preschool through primary and secondary school, including their educational and vocational career paths beyond compulsory schooling into the labor market or tertiary education. The study comprehensively assessed children’s competencies and their familial and institutional learning environments particularly across preschool and primary school (ten assessment waves). Additionally, children’s parents and teachers were interviewed. The initial sample consisted of 547 preschool children and added 528 of their classmates in primary school after enrollment. Furthermore, both after the transition from primary to secondary education and after the transition from secondary education to vocational or tertiary education, children and their parents were again tested and interviewed until the children were 18 years old (three additional assessment waves).