Recently, there has been increased attention on ways of using the classical traditions of engineering expertise in ways that further the goals of environmental protection and sustainability. Approaches to green engineering have been noted in recent years; however, important advances have not been implemented comprehensively or systematically either in the industrial sectors or by the engineering disciplines. A set of Green Engineering Principles was proposed in 2003 as framework for how engineers could move toward sustainability in their designs.

The Twelve Principles of Green Engineering allow designers to consider fundamental factors at the earliest stages as they are designing a product, process or a system. The principles should be understood as a collection of parameters in a complex system that needs to be optimized. The application and emphasis of individual principles will be largely contextual dependant on the specific conditions and circumstances of the product, process or system being designed.

• PRINCIPLE 1 - Designers need to strive to ensure all material and energy inputs and outputs are as inherently non-hazardous as possible. • PRINCIPLE 2 - It is better to prevent waste than to treat or clean up waste after it is formed. • PRINCIPLE 3 -Separation and purification operations should be a component of the design framework. • PRINCIPLE 4 - System components should be designed to maximize mass, energy and temporal efficiency. • PRINCIPLE 5 - System components should be output pulled rather than input pushed through the use of energy and materials. • PRINCIPLE 6 - Embedded entropy and complexity must be viewed as an investment when making design choices on recycle, reuse or beneficial disposition. • PRINCIPLE 7 - Targeted durability, not immortality, should be a design goal. • PRINCIPLE 8 - Design for unnecessary capacity or capability should be considered a design flaw. This includes engineering “one size fits all” solutions. • PRINCIPLE 9 - Multi-component products should strive for material unification to promote disassembly and value retention. (minimize material diversity) • PRINCIPLE 10 - Design of processes and systems must include integration of interconnectivity with available energy and materials flows. • PRINCIPLE 11 - Performance metrics include designing for performance in commercial “after-life”. • PRINCIPLE 12 - Design should be based on renewable and readily available inputs throughout the life-cycle.

To illustrate how the Twelve Principles can be applied both across scales and across engineering disciplines, this paper seeks to provide case studies from a variety of industrial sectors. While there are differences in terminology between those who design molecules versus those who design cars, the fundamental approaches and guidelines are common among designers. By illustrating how the framework has worked in the past, it can provide a blueprint for how these guidelines can be used in future designs of products, processes, and systems.