A novel class of living radical polymerization using amines as organic catalysts was developed. It is based on a new reversible activation mechanism, reversible complexation (RC). The polymer molecular weight and its distribution (M(w)/M(n) = 1.1-1.4) were well controlled in the polymerizations of methyl methacrylate (MMA), styrene, acrylonitrile, and some functional methacrylates with a fairly high conversion in hours in many cases. The catalysts include such common amines as triethylamine and tetramethylethylenediamine (TMEDA). Their low cost, good environmental safety, and ease of handling may be attractive for possible applications. Kinetic studies supported the RC mechanism. The activation rate constant for the MMA/TMEDA. system was large enough to explain why the system provides low-polydispersity polymers from an early stage of polymerization.