The World Commission on Environment and Development (the Brundtland Commission), defined "sustainable development" as follows in the report Our Common Future (Oxford : Oxford University Press, 1987): "Sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs. It contains within it two key concepts: the concept of "needs", in particular the essential needs of the world's poor, to which overriding priority should be given; and the idea of limitations imposed by the state of technology and social organization on the environment's ability to meet present and future needs." Sustainability can encompass many things and can be pursued on several different levels and scales.