Simplistic presentations of Bronfenbrenner's ecological systems theory focus on its attention to context. Although this accurately represents the first phase of Bronfenbrenner's work, it is argued that the core feature of Bronfenbrenner's later work is its attention to the patterning and interrelationship of multiple determinants of development and on the active role of the developing person. After a review of key elements of the development of Bronfenbrenner's work, current research on

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... monitoring and knowledge is discussed as embodying many of the core elements of systems theory. Bronfenbrenner's The Ecology of Human Development: Experiments by Nature and Design (1979) summarized decades of theory and research about the fundamental processes that guide life-span development. Unlike most other recent statements of theory, Bronfenbrenner's book did not focus on a specific domain such as social relations or cognition or biological development. Instead, Bronfenbrenner focused on a scientific approach emphasizing the interrelationship of different processes and their contextual variation. Although Bronfenbrenner used this text to develop 50 specific hypotheses concerning developmental processes from infancy through adulthood, these hypotheses have only rarely been tested. Rather, the importance of Bronfenbrenner's (1979) The Ecology of Human Development and his importance in the field of developmental science are usually summarized in one of two related ways. First, Bronfenbrenner is often credited with bringing attention to contextual variation in human development and helping to move developmental psychology from "the science of the strange behavior of children in strange situations with strange adults for the briefest possible periods of time" (1977, p. 513) to more "ecologically valid" studies of Requests for reprints should be sent to Nancy Darling, Psychology