The electrical conductivity of copper (I) iodide was investigated between 50 and 450 degrees C by ac measurements at different frequencies and four-point de experiments. The resistance and capacitance of the phase boundary copper/copper iodide depend exponentially on temperature. The interfacial resistance is practically negligible in the alpha- and beta-phases, whereas the interfacial capacitance is very high. The electrical conductivity is in good agreement with previous electrochemical experiments. The enthalpy of formation of Frenkel defects and enthalpies of migration of copper vacancies and interstitials in copper iodide are reported.