Bioecological theory, developed by Urie Bron-fenbrenner, consists of a complex system integrating four fundamental components (process, person, context, and time) involved in the course of human development. This entry briefly summarizes the three phases in the development of bioecological theory and presents some of its principal concepts. It focuses on the importance of proximal processes in early childhood, emphasizing the conditions under which they can be predictive of good developmental outcomes for children. It also points out the theory’s importance for public policies.