Hydrogen Peroxide or hydrogen peroxide (H2O2) is an oxidizer commonly used as a bleach. It is the simplest peroxide (a compound with an oxygen-oxygen single bond). Hydrogen Peroxide is a clear liquid, slightly more viscous than water, that appears colorless in dilute solution. It is used as a disinfectant, antiseptic, oxidizer, and in rocketry as a propellant. The oxidizing capacity of Hydrogen Peroxide is so strong that it is considered a highly reactive oxygen species.

Hydrogen Peroxide is naturally produced in organisms as a by-product of oxidative metabolism. Nearly all living things (specifically, all obligate and facultative aerobes) possess enzymes known as peroxidases, which harmlessly and catalytically decompose low concentrations of hydrogen peroxide to water and oxygen.

For industrial applications uses, Hydrogen Peroxide is used for pulp- and paper-bleaching. It is used as mild bleaches in laundry detergents. It is used in the production of certain organic peroxides such as dibenzoyl peroxide, used in polymerisations and other chemical processes.

Hydrogen Peroxide is also used in the oil and gas exploration industry to oxidize rock matrix in preparation for micro-fossil analysis.