The implementation of thin-film technologies in energy-related applications, such as special fuel cells and gas separation membranes for low-emission power plants, is essential in terms of enhancing the functionality, reducing operating temperatures, and increasing lifetime. Introducing thin electrolyte layers into solid oxide fuel cells (SOFCs) decreases the internal cell resistance and thus drastically enhances the power density. This supports the goal of reducing the operation temperature from ~800°C to temperatures below 700°C. As the operation temperature is lowered, the temperature-activated degradation processes are slowed down, and 40,000 h of operation becomes feasible. Reducing the thickness of the gas separation membranes also reduces internal losses, and therefore, the rate-limiting steps within the layer. Thinner functional layers possess higher permeabilities but also involve a risk of more layer defects. This also holds for the fuel cells. Thus, the manufacturing of the supports and the intermediate layers is also very important. The paper gives an overview of the application of thin-film technologies to SOFCs and gas separation membranes and highlights the efforts to date. Examples include SOFC stacks operated stably for in excess of 40,000 h and submicron-sized membranes with high permeability and good separation factors.