The most often quoted definition comes from the UN World Commission on Environment and Development: “sustainable development is development that meets the needs of the present without compromising the ability of future generations to meet their own needs.”
Sustainable practices support ecological, human, and economic health and vitality. Sustainability presumes that resources are finite, and should be used conservatively and wisely with a view to long-term priorities and consequences of the ways in which resources are used. In simplest terms, sustainability is about our children and our grandchildren, and the world we will leave them.
Some other definitions of sustainability:
During her 2021-2022 term, ALA President Patty Wong focused on sustainability as one of her four presidential pillars. In her inaugural speech, President Wong outlined this area of focus, saying:
Sustainability was adopted as one of ALA's Core Values of Librarianship by ALA Council in 2019, based on the 2018 recommendations of the ALA Special Task Force on Sustainability.
This introductory page of the Sustainability and Libraries resource guide highlights activities from the American Library Association that focus on sustainability as a core value of librarianship. Other pages of the guide provide resources on sustainability, including a bibliography of recent titles and online resources.
25 Ready-To-Use Sustainable Living Programs for Libraries by 
Going Green: Implementing Sustainable Strategies in Libraries Around the World by 
