In the active condition, corrosion of titanium is controlled by activation polarization. The metal presents a surface with a low exchange current for a variety of electrochemical reactions. Low exchange currents are not conducive to establishment of passivity. However, this is overcome by unusually active critical potentials for passivity. This accounts for the ease with which titanium is passivated by many substances which are only slightly oxidizing. It also explains the ease with which the metal can be protected anodically by galvanic coupling to other metals and alloys. Anodic deposition of thick titanium oxide films is observed under some experimental conditions.