The use of benzotriazole as a corrosion inhibitor is briefly reviewed and the theory of its mode of protection for copper in aqueous conditions is considered. The solubility has been found to increase with temperature, and the addition of benzotriazole decreased the pH and increased the conductivity of distilled water. It has been shown to be a good inhibitor for copper and brass when added to many acidic, neutral, and alkaline solutions, and it appears to act as a weak buffer. Copper surfaces pretreated with a hot solution of benzotriazole were found to have an increased resistance to staining in atmospheric environments and also to corrosion when immersed in many solutions of acids and salts. The inhibitor reduced the dissolution of copper in water and thus the pitting of aluminum foil immersed in the same water.