Piezoelectric wafer active sensors (PWAS) are inexpensive, non-intrusive un-obtrusive devices that can be surface-mounted on existing structures, or inserted between the layers of a new composite structure. The PWAS can be used in both active and passive modes. In active mode, the PWAS generate Lamb waves that can either be traveling waves or standing waves. Guided Lamb waves can travel for long distances in thin-wall structures. They can be either quasi-axial (S0), or quasi-flexural (A0) as shown. The PWAS generated Lamb waves can be used to implement most of the conventional ultrasonic techniques, such as pulse-echo, pitch-catch, and phased array. We illustrate the use of PWAS generated Lamb waves in the pulse-echo mode on an aging aircraft panel with characteristic structural details and a simulated 12.5 mm crack. Also illustrated is the use of PWAS arrays to generate a sweeping interrogation beam of Lamb waves that acts as ”structural radar”. As standing waves, PWAS generated Lamb waves are used in conjunction with the electro-mechanical (E/M) impedance technique that allows local-area damage detection. The electro-mechanical (E/M) impedance technique permits the direct measurement of the high-kHz drive-point mechanical impedance spectrum as seen by a PWAS mounted on the structure. The excitation at hundreds of kHz generates standing Lamb waves that represent localized structural modes, which are highly sensitive to incipient damage. Due to the high kHz bandwidth, such spectra are impervious to noise and disturbances originating from normal aircraft operation, which characteristically happen at most in the low kHz range. For this reason, the E/M impedance method offers good opportunities for identification of incipient local damage during the vehicle structural health monitoring process. Illustration of both traveling waves and standing waves approaches to damage detection on a realistic aircraft panel with simulated cracks is presented.