The highly active, versatile, and photoresponsive controlled/living radical polymerizations were developed using Mn-2(CO)(10) coupled with an alkyl iodide initiator (R-I) under weak visible light. The photoinduced polymerization of vinyl acetate (VAc) proceeded very fast even at 40 degrees C with a catalytic amount of Mn-2(CO)(10) (0.025 mol% of VAc or 5.0 mol % of R-I) and completed within a few hours to live the polymers with controlled molecular weights up to 10(5). The controlled polymerization was photoresponsive; that is, the polymerization proceeded only during the lighting period while maintaining the controlled molecular weights for the entire period. This system was also effective in controlled radical polymerizations of conjugated monomers such as styrene and methyl acrylate in conjuction with an appropriate alkyl iodide initiator. The contributions of the metal-catalyzed and the degenerative iodine transfer process were also examined by analyzing the model reactions.