Redox-active polymers are deeply involved in our lives in various forms, such as in displays, for energy storage, and in actuators. Besides, the unique redox properties derived from the macromolecular structure have garnered a high level of attention. In this chapter, the recent development of redox-active polymeric materials is described. The chapter is divided into several sections based on the types of redox-active polymers, namely conjugated polymers, nonconjugated polymers with redox-active units, and polymers bearing both of these features. The unique redox properties of various polymers are summarized to highlight the difference from those of small molecular counterparts.