The structural integrity of high-temperature metallic and ceramic coatings is of critical importance in meeting their intended performance and durability requirements. The integrity is adversely affected by the presence of defects, some of which may be in the as-deposited coatings as a result of processing aberrations, whereas others develop in use. Defect characteristics of metallic coatings include mechanical damage, contaminated interfaces, interfacial disbond, transverse and longitudinal cracks within the coatings, local lack of coatings, density and thickness variations, internal oxidation, oxidation and corrosion product accumulation at the interface, and excessive porosity and inclusions. In addition to some of these defects, ceramic coatings may exhibit discontinuity in deposition, misorientation of columnar structures, and infiltration by foreign materials. Whereas statistical process development and stringent quality control may eliminate the majority of these defects in as-processed coatings, the others need to be identified by routine destructive and nondestructive inspection (NDI). Destructive inspections tend to be expensive, particularly for gas turbine hardware, due to their high cost. Use of NDI techniques, therefore, is very attractive. However, in contrast to bulk structural alloys, the number of NDI techniques successfully applied to coatings is very limited.