In chemistry, the alkoxy group is an alkyl group which is singularly bonded to oxygen; thus R−O. Denoted usually with apostrophe('). The range of alkoxy groups is vast, the simplest being methoxy (CH₃O−).^[1] An ethoxy group (CH₃CH₂O−) is found in the organic compound ethyl phenyl ether (C₆H₅OCH₂CH₃, also known as ethoxybenzene).

Related to alkoxy groups are aryloxy groups, which have an aryl group singularly bonded to oxygen such as the phenoxy group (C₆H₅O−).

An alkoxy or aryloxy group bonded to an alkyl or aryl (R−O−R') is an ether. If bonded to H it is an alcohol.

An alkoxide can refer to salts of alcohols, and they are ionic compounds containing an alkoxide ions RO⁻; it is a derivative of an alcohol where the hydrogen of the –OH group is replaced by a metal,^[2] for example sodium salt of ethanol (CH₃CH₂OH) is sodium ethoxide, containing ethoxide anions CH₃CH₂O⁻ and sodium cations Na⁺.