A catalyst composition for the polymerization of radically polymerisable monomer is disclosed, which comprises (i) an initiator having a radically transferable atom or group and (ii) a component of Formula (I): {Fe[T]L}.(T/b)X, wherein Fe is iron and T its oxidation state, L is a ligand of Formula (II): R 1—N═CH—(CH 2 ) n —CH═N—R 2, in which R 1 and R 2 are independently selected from C 1 C 10 alkyl, aryl and substituted aryl, and n is 0 or 1; X represents an atom or group covalently or ionically bonded to Fe; b is the valency of the atom or group X.