ATRP reagents, including organic halides as initiators and transition metal complexes as carriers of halogen atoms, enable controlled free radical polymerization through a reversible dynamic equilibrium between active and dormant species. ATRP has fast reaction rates, moderate reaction temperatures, a wide range of applicable monomers, and powerful molecular design capabilities. These reagents are essential for the synthesis of polymers with controllable structures and tunable properties, and are used in materials science, biomedical engineering, and electronics.