In the past decade, fuel cell technology has been moving steadily towards commercialization, with prospects of high production volumes, in particular in electric vehicle applications. However, the cost and durability of the currently-used materials and components fall short of the requirements for large-scale industrialization. The development of alternative, more cost-effective materials with competitive performance and durability attributes is therefore ongoing. Radiation-induced graft copolymerization (“radiation grafting”) is a versatile method to modify pre-existing polymers to introduce a variety of desired functionalities, such as ion-exchange capacity. Here, an overview of fundamentals and recent developments in the area of radiation grafted ion-conducting polymers for application in polymer electrolyte fuel cells (PEFCs) is provided. Key aspects of polymer design are discussed, taking into consideration the radiation chemistry of base polymer materials and the adequate choice of grafting monomers for different PEFC types. Furthermore, the current status of applications in fuel cells is highlighted.