Between 1970 and 1990 Dr. Uri Bronfenbrenner proposed and revised a theory that focused on understanding human development as occurring within nested and interconnected systems ranging from family, friends, and teachers out to the community, state, and culture. The systems interact across time and impact, and are impacted by, the developing individual through their lifespan. This "Ecological Systems Theory" has had major impacts on research and policy. The theory includes a set of specific propositions and hypotheses. I believe that many of the ideas within the theory apply not only to a broad view of human development, but also have relevance for understanding teaching and teacher education. Blogs in this section will describe ways in which Bronfenbrenner's ideas might provide ways for designing and evaluating teacher preparation and for better understanding effective teaching and mentoring relationships.