Sodium hypochlorite, commonly known in a dilute solution as (chlorine) bleach, is an inorganic chemical compound with the formula NaOCl (or NaClO), comprising a sodium cation (Na⁺
) and a hypochlorite anion (OCl⁻
or ClO⁻
). It may also be viewed as the sodium salt of hypochlorous acid. The anhydrous compound is unstable and may decompose explosively. It can be crystallized as a pentahydrate NaOCl·5H
₂O, a pale greenish-yellow solid which is not explosive and is stable if kept refrigerated.

Sodium hypochlorite is most often encountered as a pale greenish-yellow dilute solution referred to as liquid bleach, which is a household chemical widely used (since the 18th century) as a disinfectant or a bleaching agent. In solution, the compound is unstable and easily decomposes, liberating chlorine, which is the active principle of such products. Sodium hypochlorite is the oldest and still most important chlorine-based bleach.

Its corrosive properties, common availability, and reaction products make it a significant safety risk. In particular, mixing liquid bleach with other cleaning products, such as acids found in limescale-removing products, will produce chlorine gas, which was used as a chemical weapon in World War I. A common urban legend states that mixing bleach with ammonia also releases chlorine, but in reality the two chemicals react differently, producing chloramines and/or nitrogen trichloride. With excess ammonia and sodium hydroxide, hydrazine may be generated.