Acetic acid bacteria (AAB) are bacteria that derive their energy from the oxidation of ethanol to acetic acid during fermentation. They are Gram-negative, aerobic, rod-shaped bacteria. They are not to be confused with the genus Acetobacterium, which are anaerobic homoacetogenic facultative autotrophs and can reduce carbon dioxide to produce acetic acid, for example, Acetobacterium woodii.

The acetic acid bacteria are usually airborne and are ubiquitous in nature. They are actively present in environment where ethanol is being formed as a result of fermentation of sugars. They can be isolated from the nectar of flowers and from damaged fruit. Other good sources are fresh apple cider and unpasteurized beer that has not been filter sterilized. In these liquids, they grow as a surface film due to their aerobic nature and active motility. Vinegar is produced when acetic acid bacteria act on alcoholic beverages such as wine. Fruit flies or Vinegar eels are considered as a common vector in propagating acetic acid bacteria in nature.

Acetic acid  /əˈsiːtɨk/ (systematically named ethanoic acid  /ˌɛθəˈnoʊɨk/) is an organic compound with the chemical formula CH₃CO₂H (also written as CH₃COOH). It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar (apart from water), and has a distinctive sour taste and pungent smell. It is mainly produced as a precursor to polyvinylacetate and cellulose acetate. Although it is classified as a weak acid, concentrated acetic acid is corrosive, and attacks the skin.

Acetic acid is one of the simplest carboxylic acids. It is an important chemical reagent and industrial chemical, mainly used in the production of cellulose acetate mainly for photographic film and polyvinyl acetate for wood glue, as well as synthetic fibres and fabrics. In households, diluted acetic acid is often used in descaling agents. In the food industry, acetic acid is used under the food additive code E260 as an acidity regulator and as a condiment. As a food additive it is approved for usage in the EU, USA and Australia and New Zealand.