Combining reversible-deactivation radical polymerization (RDRP) techniques in a single system provides access to exciting new polymeric materials which would be difficult to obtain by other means. Dual RDRP agents are species which can undergo two (or more) distinct RDRP processes sequentially without any chemical transformations between the polymerization steps. By incorporating multiple controlling functions in the same species, dual agents offer elegant pathways to functional polymers without resorting to end-group conversions or coupling of pre-formed polymers. Dual agents have been used to synthesize a range of innovative structures such as well-defined block copolymers from monomers with disparate reactivities, degradable drug delivery vehicles and surface-tethered brushes which both exploit mid-chain functionality, complex architectures such as bottlebrush, star, and multiblock copolymers, and novel nanoparticles in which the controlling functions are physically isolated through self-assembly. The present review highlights the state of the art of dual systems, with a particular emphasis on orthogonality considerations and the potential of dual agents for accessing new polymeric materials.