Diffraction techniques are particularly suited for the study of the structural and mechanical properties of ceramic thermal barrier coatings (TBCs) for applications in engine components. Both X-ray (lab and synchrotron radiation) and neutron diffraction permit a non-destructive determination of phase content and several interesting related properties. Besides identification and quantitative phase analysis, detailed information can also be obtained on the residual strain field, both on the surface of the coating and through entire coated components, and on possible texture of deposited layers. This type of analysis is especially important for the design and production of TBCs, as well as for determination of the useful life of coated components. Some of the methodologies described in this work can be applied on a routine basis for quality control at the industrial level.