Abstract: A high-temperature seal having in-situ integrity monitoring capability includes a quantity of dielectric material sealing an interface between adjacent structures and an electrical transmission line embedded within the dielectric material. A signal injection port is provided for exciting the transmission line with an excitation signal. One or more sample ports are provided for sampling the transmission line to obtain signal samples resulting from the excitation signal. The sample port(s) are adapted for connection to a signal analyzer adapted to analyze the signal samples for indications of seal integrity problems. Using a technique such as time domain reflectometry or frequency response analysis, the transmission line can be monitored for changes in characteristic impedance due to changes in seal dielectric constant and/or disruption of the transmission line.