Tetradentate amine-bis(phenolate)iron(III) halide complexes containing chloro substituents on the aromatic ring are extremely efficient catalysts for controlled radical polymerization. Molecular weights are in good agreement with theoretical ATRP values, and dispersities are as low as 1.07 for substituted styrenes and methyl methacrylate polymerizations. Kinetic data reveal activity for styrene polymerization among the fastest reported to date, with the excellent control shown to be electronic rather than steric in origin. Mechanistic studies implicate a multimechanism system with cooperation between atom transfer radical polymerization (ATRP) and organometallic mediated radical polymerization (OMRP). The in situ reduction of the Fe(III) complex with ascorbic acid or tin octanoate allows polymerizations to be initiated by both 1-phenylethyl chloride (1-PECI, ATRP regime) and azobis(isobutyronitrile) (AIBN, OMRP regime) to isolate the mechanism of control and offer unique initiation pathways.