Thermodynamic data for reactions concerned in the corrosion of copper in waters containing dissolved oxygen and carbon dioxide are assembled and are used to demonstrate certain features of the corrosion processes. These include the extreme vulnerability of copper to attack, the critical effects of oxygen, and the inadequately protective properties of films of solid corrosion products. Confirmation and extension of these conclusions are obtained by experimental studies of systems derived from copper, cuprous oxide, cupric oxide, malachite, and azurite in water kept in equilibrium with gaseous atmospheres containing known partial pressures of oxygen and carbon dioxide. It is shown, inter alia, that cuprous oxide is highly susceptible to dissolution, both by disproportionation and oxidation, and that metallic copper dissolves in such media at a constant rate, despite the accompanying film growth, accumulation of cupric bicarbonate in solution, and rise of pH. The maximum rate of dissolution is attained at a molar ratio of in the gas phase, when a substantial oxide film is formed on the metal.