A nondestructive evaluation (NDE) technique based on electrochemical impedance spectroscopy (EIS) is developed for concrete beams strengthened with carbon fiber reinforced polymer (CFRP) sheets to detect the debonding of CFRP from concrete. Copper tape on the surface of the CFRP sheet, stainless steel wire embedded in the concrete, and reinforcing bars were used as sensing elements. In laboratory experiments, the CFRP was progressively debonded using a wedge and impedance measurements were taken using various pairs of electrodes. Changes in the impedance spectra, and the capacitance parameters obtained from equivalent circuit analysis, can be used to assess the global state of the bond between CFRP and concrete. Impedance measurements taken between embedded wire sensors can be used to locate debonded regions. Preliminary finite element simulations are performed to elucidate the experimental observations.