In a study of the application of alkenylsuccinic acids (ASA's) as leather-waterproofing agents the following observations were made: (a) only liquid ASA's are effective, (b) leather treated with ASA is not water-repellent; rather it absorbs water readily, (c) the water resistance of leather treated with ASA is affected less by surfactants than leather treated with silicones, (d) ASA does not react strongly with leather, and (e) ASA's are water-in-oil emulsifiers. Based on these observations it is postulated that ASA's function by forming a viscous water-in-oil emulsion within the interstices of the leather upon exposure to water. In confirmation of this theory it was found that certain commercial water-in-oil emulsifiers are also effective waterproofing agents.