The present state of the chemistry of extraction equilibria involving sulphoxides of diverse structure — aliphatic, cyclic, and also mixtures of petroleum origin — is discussed, and results are given for the extraction of inorganic and organic acids and metal salts from aqueous solution. Comparison of the extraction properties of neutral organophosphorus compounds with those of sulphoxides shows a promising future in liquid extraction for cyclic sulphoxides, especially those of petroleum origin. The mechanism of extraction is discussed, and the dependence of extraction properties on the molecular structure of the sulphoxide is considered. A list of 153 references is included.