Traditional methods capable of measuring the corrosion rate of reinforcing steel in concrete require electrical contact to the steel and are therefore destructive in cases where contact is only accessible through drilled holes into the concrete cover. Studies have shown that the application of an electric field to the surface of an electrolytic medium can indirectly polarize a metal within the solution.1 Based on this concept, an indirect impedance measurement may be used to assess the properties of steel reinforcement within concrete without an electrical contact.2,3 A four-electrode array is placed on the concrete surface and the perturbation signal is applied between the outer two electrodes while the response is measured between the inner two electrodes. As shown in the figure provided, the electrode configuration results in a nonuniform current distribution in which a portion of the injected current goes through the concrete and another portion goes through the steel. The result is an impedance response that while capable of sensing corrosion properties of the steel, is also confounded by the properties of the concrete. Therefore, challenges arise in relating the measured impedance of the system to the impedance of the steel-concrete interface. One of the challenges is establishing the sensing location and polarized surface area of the steel. Another challenge lies in determining the appropriate contribution of the concrete to the measured impedance.This tutorial will provide a detailed description of the indirect impedance method including experimental design considerations, measurement approaches, analysis methods, and potential complications. A calibration method will be presented to relate the apparent polarization resistance to the actual polarization resistance and therefore circumvent the challenge of quantifying the steel sensing area. The necessary assumptions of the calibration procedure will be described. C. Andrade, I. Martinez, and M. Castellote. "Feasibility of determining corrosion rates by means of stray current-induced polarisation." Journal of applied electrochemistry 38, no. 10 (2008): 1467-1476.J. Monteiro, H. Morrison, Non-destructive method of determining the position and condition of reinforcing steel in concrete, 1999. US Patent 5,855,721.M Keddam, X. R. Novoa, V. Vivier, “The concept of floating electrode for contact-less electrochemical measurements: Application to reinforcing steel-bar corrosion in concrete,” Corrosion Science, 51 (2009) pg. 1795-1801. Figure 1