Tertiary amines were found to remarkably enhance the catalytic activity of ATRP catalysts CuBr/tris[(2-pyridyl)methyl]amine and CuBr/tris[2-(dimethylamino)ethylamine]. These two catalysts alone failed to polymerize AAA, MMA, and styrene at reduced catalyst concentrations. With tertiary amines such as triethylamine both catalysts could mediate fast polymerizations of the three monomers in a controlled manner at as low as 1 mol-% catalyst relative to initiator. A mechanism study showed that tertiary amines reduced copper(II) complexes to active copper(I) complexes.