For decades there hasn't been an integrative theory of development, only theories about various developmental domains such as language acquisition, personality, and peer relations. Two leading developmentalists, Donald H. Ford and Richard M. Lemer, present the first integrative theory on human development. Through a synthesis of developmental contextualism and the Living Systems Framework, the authors develop a theory that examines how a person carries out transactions with their environment and through that transction how their biological, psychological, behavioral, and environmental elements change or remain constant. They also offer important implications of Developmental Systems Theory (DST) for research, implications for use in educational and clinical settings, and the usefulness of DST in the formulation of social policy. By intergrating the result from many research investigations into a larger framework, Developmental Systems Theory offer researchers, professionals, and students a better understanding of how multiple elements interact and shape a person's life.