Gas turbines are widely used to generate electricity and to propel aircraft. Increasingly scarce resources, the need to remain competitive, and climate change are driving the UK's energy market and its aerospace industry to demand efficiency, reliability and emissions reduction. Being heat engines, the gas temperature at the entry to the turbine is required to be as high as possible to maximise efficiency, and consequently, metallic components in this part of the engine are coated in thermal barrier coatings (TBCs) to protect them from melting. Further increases in gas turbine efficiency, reliability and emissions reduction absolutely necessitate further improvements to TBCs. Optimised TBCs would allow significantly higher gas temperatures to increase efficiency and will be more durable. Part of the barrier to optimising TBCs is that a complete mechanistic understanding of TBC failure has not yet been achieved. Such an understanding would facilitate timely maintenance, avoid unplanned down time, and underpin and direct development of new optimised TBC material systems. This PhD research will achieve a mechanistic understanding of blister development and spallation in TBCs with the aim to predict and optimise TBC lifetime, increase operating temperature, and minimise lifetime variation.