To check the reproducibility of electrochemical impedance spectroscopy (EIS) measurements, nineteen laboratories have performed round-robin testing on EIS using various instruments and three different systems: a dummy cell, and two electrochemical systems of practical interest in the nuclear corrosion domain. The dummy cell consisted of a number of resistors and capacitors. The first electrochemical system was a Cu wire in CuSO4 solution and the second electrochemical system consisted of a Zr wire in Na2SO4 solution. The general conclusion drawn from the tests performed with the dummy cell is that the actual commercially available instruments for EIS measurements are suitable to produce good quality data. Differences in the EIS diagrams for the tested electrochemical systems, especially for the Cu/CuSO4 system, were observed and discussed. This round-robin exercise, involving for the first time a large number of laboratories, shows that intrinsic scatter (large or small) is present in the impedance data and that reproducibility should be readily checked. While EIS is an excellent technique for investigating the kinetics of electrochemical systems, great care has to be taken on planning and conducting the experiments, which in fact should be valid for all testing techniques. Recommendations are given in this paper to help obtaining reliable EIS results.