Extensive research over recent decades has demonstrated the feasibility of producing stable radical polymers (SRPs) by exploring structure–stability relationships. Owing to their excellent redox activities and inherent paramagnetic characteristics, SRPs are emerging as key functional materials with considerable potentials for various applications such as in organic electrodes, semiconductors, magnetic materials, and quantum information technologies. Accordingly, this review provides a comprehensive summary of the most widely investigated and representative families of SRPs. Innovative strategies for the design and synthesis of SRPs and the relationship among the physicochemical properties, electronic structures, and resulting functionalities of these polymers are discussed. Moreover, recent advancements in the applications of SRPs are highlighted. Finally, the key challenges in radical chemistry and material functionalization, offering insights into the transformative potential of these materials for future applications, are emphasized.