A substantial research effort has been devoted to the investigation of mechanisms that dictate the durability of thermal barrier systems used to protect metallic components in gas turbines. Thermal barrier coatings (TBCs) are widely used, with demonstrated performance attributes, but they are susceptible to delayed failure by way of cracking, buckling, delamination and spalling. These coating systems are complex materials, comprising multiple layers having disparate thermo-elastic properties, and experiencing severe cyclic thermal exposure. Residual stresses that develop due to microstructural evolution, oxide growth and thermal mismatch are the principle drivers for coating failure. The continuous growth of an oxide layer at the ceramic/metal interface during service is of key importance. The compressive stresses that develop in this layer, and their interaction with morphological features, motivate the overall crack nucleation and damage evolution. For a particular thermal barrier system, failure occurs by way of a displacement instability in the thermally grown oxide (TGO). Experimental observations characterizing the damage evolution and failure mechanisms for such a system will be discussed. Indentation test protocols, coupled with high-resolution imaging and spectroscopic techniques, are used to quantify fracture characteristics of the multi-layer TBC structures. The mechanisms controlling the continuous growth of the oxide layer in TBC systems is of particular interest. Key issues include the overall oxide growth rate, the location at which new oxide forms, the influence of metallic surface preparation and oxidation environment, and the resulting oxide layer microstructure. Systematic studies of oxide growth under varying surface preparation and environemental conditions are discussed, with emphasis on how the details of the oxide growth effect the mechanics of damage evolution. A novel mechanics-based test methodology providing insights into oxide growth mechanisms will be described. The experimental findings are correlated with models and simulations to capture and quantify the important parameters affecting system durability. Implications of the research for the design of thermal barrier systems with improved durability will be discussed.