A substance that can biodegrade is one that can decay over time, or be absorbed by the environment by natural or biochemical means. Most organic wastes and paper, for example, can be broken down by bacteria and sunlight into basic elements of nature, and thus recycled back into the ecosystem. How quickly this process occurs depends on how much of the substance is available and where it is deposited. A piece of paper left in a field, for example, will biodegrade at a much higher rate than one compacted into a landfill with several pounds of other wastes.

Some substances do not naturally biodegrade in the environment, which primarily include those created through synthetic means. Most plastics fall into this category.