"The quest for intermediate-temperature solid oxide cell air electrodes has led to novel compositions and microstructures, new surface activation strategies, as well as smart nanostructures composed either of materials with different functionality or single compositions with distinct grain cores surrounded by high ionically conducting grain boundaries. In this chapter, we report on the most novel concepts and latest developments carried out in the field towards the development of air electrodes with better performance and stability. We also focus on the current, often contradictory, understanding of the intrinsic and extrinsic factors affecting the oxygen reduction reaction, the origin of the detrimental surface segregation and the various concepts proposed to limit common electrode degradation processes. Finally, we also give some hints on the expected prospects in the field. The advent of new multimodal, in situ and operando techniques, combined with combinatorial and machine-learning approaches, will allow us to envisage a significant improvement in the air electrodes' performance in the near future."