A preservative is a naturally occurring or synthetically produced substance that is added to products such as foods, pharmaceuticals, paints, biological samples, wood, etc. to prevent decomposition by microbial growth or by undesirable chemical changes.

Preservatives may be added to wood to prevent the growth of fungi as well as to repel insects and termites. Typically arsenic, copper, chromium, borate, and petroleum based chemical compounds are used. For more information on wood preservatives, see timber treatment.

Preservative food additives can be used alone or in conjunction with other methods of food preservation. Preservatives may be antimicrobial preservatives, which inhibit the growth of bacteria or fungi, including mold, antioxidants such as oxygen absorbers, which inhibit the oxidation of food constituents. Common antimicrobial preservatives include sorbic acid and its salts, benzoic acid and its salts, calcium propionate, sodium nitrite (and sodium nitrate which converts to sodium nitrite "in situ"), sulfites (sulfur dioxide, sodium bisulfite, potassium hydrogen sulfite, etc.) and disodium EDTA. Antioxidants include BHA, BHT, TBHQ and propyl gallate. Other preservatives include ethanol and methylchloroisothiazolinone. FDA standards do not currently require fruit and vegetable product labels to reflect the type of chemical preservative(s) used on the produce.^{[citation needed]} The benefits and safety of many artificial food additives (including preservatives) are the subject of debate among academics and regulators specializing in food science, toxicology, and biology.