Microstructure and phase constituents of five different commercial production thermal barrier coatings (TBCs) were characterized by using transmission electron microscopy (TEM) and related analytical techniques such as X-ray Energy Dispersive Spectroscopy, selected area diffraction, convergent beam electron diffraction, high angle annular dark field imaging in scanning TEM, and high resolution TEM. The TBC specimens examined in this study were produced by different processing methods: air plasma spray and electron beam physical vapor deposition for Yttria Stabilized Zirconia (YSZ) top coat; low pressure plasma spray and chemical vapor deposition for NiCoCrAlY and (Ni,Pt)Al bond coat. The as-coated microstructure and phase constituents were examined as a function of processing methods. The evolution of microstructure, void formation and phase constituents, particularly for the thermally grown oxide scale is presented as a function of furnace thermal cycling.