In chemistry, an alcohol is any organic compound in which a hydroxyl group (-OH) is bound to a carbon atom of an alkyl or substituted alkyl group. The general formula for a simple acyclic alcohol is C_nH_2n+1OH.

Other alcohols are usually described with a clarifying adjective, as in isopropyl alcohol (propan-2-ol) or wood alcohol (methyl alcohol, or methanol). The suffix -ol appears in the "official" IUPAC chemical name of all alcohols.

There are three major subsets of alcohols: primary (1°), secondary (2°) and tertiary (3°), based upon the number of carbon atoms the C-OH group's carbon (shown in red) is bonded to. Ethanol is a simple 'primary' alcohol. The simplest secondary alcohol is isopropyl alcohol (propan-2-ol), and a simple tertiary alcohol is tert-butyl alcohol (2-methylpropan-2-ol).

The word alcohol was introduced into the English language circa 1543 from the Arabic: الغول‎, "al-ġuḥl". In layman's terms, it usually refers to ethanol, also known as grain alcohol or (older) spirits of wine, or to any alcoholic beverage.

Carbohydrates (sugars) and sugar alcohols are an important class of compounds containing multiple alcohol functional groups. For example, sucrose (common sugar) contains eight hydroxyl groups per molecule and sorbitol has six. Most of the attributes of these polyols, from nomenclature, to occurrence, use and toxicity, are sufficiently different from simple aliphatic alcohols as to require a separate treatment.

The simplest and most commonly used alcohols are methanol and ethanol. Methanol was formerly obtained by the distillation of wood and called "wood alcohol." It is now a cheap commodity, the chemical product of carbon monoxide reacting with hydrogen under high pressure.^{[citation needed]} Methanol is intoxicating but not directly poisonous.