Real-time structural integrity monitoring is a concept that is becoming a reality in the engineering community. It will soon be possible for a structure to warn the user when its own structural integrity has been altered. A qualitative impedance-based health monitoring technique, which can be implemented for real-time damage evaluation of complex structures, is investigated. The basic principle of the technique is to monitor the structure's mechanical impedance which will be changed with the presence of damage. The mechanical impedance variations are monitored by measuring the electrical impedance of a bonded piezoelectric actuator/sensor (PZT). This mechanical-electrical impedance relation is due to the electro-mechanical coupling property of piezoelectric materials. This health monitoring technique can be easily adapted to existing structures, since only a small non-intrusive PZT patch is needed. This impedance-based method operates at high frequencies (generally above 100kHz), which enables it to detect incipient type damage in a localized region. The localized sensing region offers the advantage of not being affected by nonnal operating conditions or by changing boundary conditions. In this thesis, a complete theoretical background on the impedance-based technique is derived. Then, the technique is applied successfully to a variety of case studies; such as composite patch repair, aircraft structures, precision parts, and civil infrastructure. By simplifying the impedance measurement interpretation through a simple scalar damage metric, the real-time implementation of the impedance-based technique has been proven feasible. / Master of Science