Research into metal–air batteries is spurred by the promise of high energy densities, often surpassing those of lithium-ion batteries. Despite this promise, the development of practical metal–air batteries is hampered by their poor reversibility. Current research has indicated that the mechanisms causing battery degradation typically involve multiple aspects: 1. Whether the limiting factor in the formation/decomposition of the discharge production (such as Li2O2, in Li–O2 batteries) is e− or Li+, i.e. does the interface occur at the Li2O2/electrolyte or the electrode/Li2O2? 2. The continuous formation of production during discharge clogs the electrode pores, reducing the effective area of the cathode material and thereby diminishing the capacity of the metal-air battery. 3. The generation of intermediate active species at the cathode, such as superoxides, peroxides, and singlet oxygen (1O2), leads to corrosion of critical battery components, including the electrolyte and electrodes. This corrosion leads to the formation of numerous decomposition products that are challenging to decompose, further exacerbating battery degradation. This chapter will briefly introduce the basic mechanisms of metal–air batteries and give an overview of the causes of battery degradation. Strategies to mitigate degradation will be explored along with suggested research directions.