Recent advances in the controlled radical polymerization methods have facilitated the synthesis of well-defined functional polymers. We use reversible addition-fragmentation chain transfer (RAFT), which is one of the most versatile controlled radical polymerization technique, to afford well-defined functional polymers such as optoelectronic, amino-acid-based, and stimuli-responsive polymers. We also focus on developing unique polymerization systems (ring-opening RAFT polymerization, controlled radical polymerization of N-vinyl, S-vinyl, and ionic monomers) and macromolecular designs (e.g., star-shaped and hyperbranched polymers, amphiphilic block copolymers, and alternating copolymers).