Several X-ray backscattering methods have been recently developed for process-control and quality-assurance measurements in applications where thin coatings are applied to much thicker substrates. X-ray fluorescence (XRF) techniques have been developed for some aerospace applications where many differing layers are sequentially applied to the same substrate. The measurements were carried out utilizing suitable inherent tag elements either in the layer being applied or in one or more of the layers underneath. The suitability of certain tag elements is discussed for given coating thickness ranges, material composition and required sensitivity and throughput. Some specific examples are presented. In addition, a contact-film radiographic technique has been developed for localized porosity measurements in applications where the coating material and substrate differ significantly in average atomic number. Photoelectrons stimulated by a highly filtered X-ray field are used to produce a high-resolution radiograph of the localized porosity defects. Both of the methods represent measurement techniques that have been optimized for specific gauging applications.