A biocide is a chemical substance capable of killing different forms of living organisms used in fields such as medicine, agriculture, forestry, and mosquito control.

A biocide can be:

A pesticide, which includes fungicides, herbicides, insecticides, algicides, molluscicides, miticides and rodenticides.

An antimicrobial, which includes germicides, antibiotics, antibacterials, antivirals, antifungals, antiprotozoals and antiparasites. See also spermicide.