At present, the biggest hurdle for the commercialization of fuel cells is the correlated manufacturing cost, where the expense on the cathodic oxygen reduction electrocatalysts holds a large portion. It is because the precious platinum (Pt) and its alloys are still the most effective oxygen reduction reaction (ORR) catalysts, which play an essential role in deciding the overall performance of a fuel cell. In this chapter, we present an overview on recent progresses in the development of defective ORR electrocatalysts for fuel cell applications. Particularly, we introduce a totally new theory regarding the ORR, a defect catalysis mechanism, which is proved to be more effective than the commonly accepted heteroatom‐doping mechanism. Meanwhile, we summarize several typical defective carbon‐based, cost‐effective ORR catalysts, such as metal–organic‐framework‐derived defective carbons, defective graphene, and defective activated carbon. In addition, other defective carbons, such as carbon nanotubes enriched with edge defects, carbon nanocages with intrinsic carbon defects, and defective graphene with nitrogen dopant, will be summarized as well. These defective‐based carbons are obviously much cheaper than that of the commercial Pt/C and are the potential ORR catalysts to be used for fuel cell applications.