Metal-air batteries, especially the rechargeable type, are currently of great interest for many industrial sectors. Besides the potentially low-cost zinc-air system, the potentially high-energy lithium-air system, originally intended as a high-energy storage device for electric mobility, has been investigated a lot within the last ten years. Within this article, rechargeable zinc-air and lithium-air systems will be discussed. Especially the role of the gas diffusion electrode will be described and general trends for further developments will be given.