Sustainability is based on a simple principle: Everything that we need for our survival and well-being depends, either directly or indirectly, on our natural environment. Sustainability is the capacity to meet the needs of the present without compromising the ability of future generations to meet their own needs. For humans, sustainability is the long-term maintenance of well-being while addressing the "Three E's" - economy, environment and social equity.
In 1972, a United Nations (UN) Conference on the Human Environment placed environmental issues on the international agenda for the first time. By 1983, the relationship between economic development and its impact on the environment had become the subject of inquiry by the UN World Commission on Environment and Development, known as the Brundtland Commission.
In 1987 the Brundtland Commission authored the book, "Our Common Future," which included a definition of sustainability. This definition continues as the most succinct answer to the question, "What is sustainability?"
In 1992, more than 100 heads of state met in Rio de Janeiro, Brazil for the first international Earth Summit convened to address urgent problems of environmental protection and socio-economic development. The assembled leaders signed the Convention on Climate Change, the Convention on Biological Diversity, endorsed the Rio Declaration and the Forest Principles, and adopted Agenda 21, a 300 page plan to guide cities in achieving sustainable development in the 21st century.
The Commission on Sustainable Development was then created to monitor and report on implementation of the Earth Summit agreements. It was agreed that a five year review of Earth Summit progress would be made in 1997 by the United Nations General Assembly. This special session of the UN General Assembly took stock of how well countries, international organizations and sectors of civil society have responded to the challenge of the Earth Summit.
Although Agenda 21 guidelines have not been utilized in the U.S. as extensively as they are in Europe, many U.S. cities are role-modeling sustainability in both policy and in practice. Such cities include Palo Alto, Portland, Seattle, Brookline (MA), San Diego, Santa Monica and Austin (TX). In addition, many organizations are now in place to assist local governments and businesses in achieving sustainable business practices.