The substitution principle is focused on the substitution of a product, service or process to another that is more efficient or beneficial in some way while retaining the same functionality. The prominent substitution nowadays is replacing a product, process or service in order to better the environment.

This is usually proposed by the environmental groups, although many critics claim that is very difficult to reach an operational scheme, i.e. to implement this in reality especially in terms of legislation.

substitution of non renewable resources by renewable resources is the main principle of sustainability.eg.we should substitute coal by eco-friendly energy sources like solar energyor wind energy.complete substitution is not possible always.however efforts must be made.