Maintenance personnel in the U.S. military are interested in developing methods of damage detection for composite materials that are field expedient and less dependent on the operator’s experience than the current methods. A vibration-based method was developed for detecting damage in composite materials based on a measurement of the nonlinear forced response that damaged materials are assumed to exhibit. A damage feature was extracted for a structural component by quantifying the degree to which the reciprocity between two input-output structural paths fail due to the nonlinearities associated with damage. A dynamic nonlinear theoretical model was used to develop a better understanding of why reciprocity fails for networks of nonlinear components. Experimental results were obtained from carbon fiber composite specimens subjected to various levels of damage. It was determined that reciprocity measurements were capable of identifying damage due to impact energies of 10.8 N·m; however, the method was not capable of discerning damage that was not directly beneath the sensor locations. The levels of damage that could be consistently detected using the new methodology could be discovered through a close visual inspection. In comparison to currently employed methods of damage detection, the proposed methodology is less subjective but also less sensitive to damage. More development work will be required to propose this technology as a replacement for current methods such as ultrasound and tap testing.