3.1 Sustainability
In ecology, sustainability refers to how biological systems remain diverse and productive. Long-lived and healthy wetlands and forests are examples of sustainable biological systems.

In more general terms, sustainability is the endurance of systems and processes. The organising principle for sustainability is sustainable development, which includes the four interconnected domains: ecology, economics, politics and culture.

3.2 Sustainable Development
The United Nations World Commission on Environment and Development (WCED) in its 1987 report Our Common Future [3] defines sustainable development as:

"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.

All definitions of sustainable development require that we see the world as a system—a system that connects space; and a system that connects / time

• World as a system over space - air pollution from North America affects air quality in Asia, and pesticides sprayed in Argentina could harm fish stocks off the coast of Australia.
• World as a system over / time - the decisions our grandparents made about how to farm the land continue to affect agricultural practice today; and the economic policies we endorse today will have an impact on urban poverty when our children are adults.
• Quality of life is a system, too. It's good to be physically healthy, but what if you are poor and don't have access to education? It's good to have a secure income, but what if the air in your part of the world is unclean? And it's good to have freedom of religious expression, but what if you can't feed your family? “

3.3. Design for Sustainability – Three perspectives from stakeholders

The application of Design for Sustainability can mean different aspects to the different stakeholder, depending from whose point of view one looks at the issues and parameters.

3.3.1 From a Company Perspective
As defined by UNEP (2006) D4S is – ‘a method for companies to improve profit margins, product quality, market opportunities, environmental performance, and social benefits. Companies can achieve this win-win situation for shareholders, consumers, and the public by improving efficiencies in the products and services they design, produce and deliver’.

3.3.2 D4S from an Educator and Designer Perspective
Vezzoli, et. al. (2014) defines D4S as – ‘a design practice, education and research that, in one way or another, contributes to sustainable development’.

3.3.3 From Society, Community & User Perspective
Tischner (2010) defined D4S as – ‘generating solutions that are equally beneficial to the society and communities around us (especially unprivileged and disadvantaged populations), to the natural environment, and to economic systems (globally but especially locally).’