This lecture outlines the development and core assumptions of the ecological paradigm as it has evolved in the fields of biology, sociology, psychology, and public health. The Chicago School of Human Ecology is described and contrasted with broader-gauged analyses of human ecosystems including the Sociocultural School of Human Ecology and more recent conceptualizations of Social Ecology. The Chicago School, based largely on biological and economic principles, neglected the role of psychological, cultural, architectural, and regulatory influences on peoples’ relations with their environments. The fields of social ecology and environmental psychology give greater attention to the interplay among these diverse factors, and to considerations of environmental justice and equitable access of all community members to healthful surroundings.