BiKS is an interdisciplinary longitudinal large-scale study on educational processes, competence development, and the formation of educational decisions. It consists of two panel studies: BiKS-3-18 started in September 2005 with 547 children at age 3 and followed these children till age 18 with 13 panel waves. BiKS-8-18 started in March 2006 with 2,395 students in grade 3 and followed them till age 18 with 11 panel waves. Both samples were drawn in selected cities and regions in Bavaria and Hesse (Germany) following a multi-step sampling procedure. Besides individual development of competencies, school-relevant attitudes, and educational decisions, special attention is given to the family, preschool, and school as important learning environments. The instrumentation follows a multi-informant perspective where possible and includes standardized competence tests, questionnaires, and observational methods. Moreover, some subsamples are studied with in-depth qualitative methods. Data are documented and available to the scientific community free of charge. This chapter provides a general introduction to the interdisciplinary research unit BiKS and its main aims. Moreover, it presents an overview of the two longitudinal BiKS studies BiKS-3-18 and BiKS-8-18.