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It is expected that at the beginning of the third millennium, almost half of the world population likely to live in urban areas, where most resources will be consumed and most waste and pollution would be produced. There is an agreement that the current patterns of urban development and human activity have led to global warming, greenhouse gases, ozone layer depletion, acid rain, and other environmental degradation. The Rio earth summit in 1992 came to the conclusion that such patterns of development are not sustainable in the long term without some significant changes. Under circumstances, the role of city/urban form has rapidly gained considerable attention from governments and academics for its share in terms of the lack of sustainability. Therefore it is suggested that cities should act as a locus for solving global problems towards achieving sustainability. However, there are several ambiguities and theoretical clashes in the concept and achievement of sustainability; that might be seen as a potential danger to the fulfillment of sustainable development. This paper, therefore, seeks to examine the origins of environmental theories, and the social-historical background that finally led to the sustainable development school of thought. The literature search resulted in the identification of two dominant theories in the environmental discourse: I) Technocentrism and ii) Ecocentrism that are influential in forging later urbanism and planning theories. The paper tries to explore the roots of contemporary urban planning and design theories in the light of their socio-historical backgrounds through a content analysis method. The intention here is to provide a basis for better understanding and assessing the new theories when applying them to the realms of urban planning and urban design in the new millennium