Tools are needed to define, measure and assess pollution in processes and products, to direct and measure improvements in designing cleaner processes and products, and to design benign processes and products. Life cycle assessment, process simulation and integration, material substitution and environmental impact assessment are some of these tools. Advances have been made recently in incorporating environmental criteria in process and product design, some renditions of which are commercially available. This is a compilation of methods, tools and models that can be used to design products and manufacturing processes that prevent pollution from occurring in the first place, rather than treating the wastes after they are formed. There is also a critique of social barriers to pollution prevention.