The etching process of polycrystalline tin-doped indium oxide (ITO) films in HCl solutions is investigated by kinetic and electrochemical experiments and the patterning characteristics are examined by scanning electron microscopy. The influence of oxidizing agents on the etching behavior is studied. A model is proposed in which ITO is first attacked by undissociated HCl molecules, forming a surface intermediate which is mobile on the surface. This intermediate can react with HCL molecules or with the oxidizing agent. The competition between these two reactions determines the kinetics and the patterning characteristics of the dissolution process. A kinetic rate law is derived that predicts the etch rate in FeCL(3)/HCl solutions. A good agreement between experimental and calculated values is obtained in a wide range of HCl and FeCl3 concentrations.