The controlled/living polymerization of methyl methacrylate was carried out by atom transfer radical polymerization (ATRP) in a water-borne system. Both the direct and reverse processes were performed in the presence of a copper halide/4,4'-di(5-nonyl)-2,2'-bipyridine (dNbpy) complex and a nonionic surfactant. In direct ATRP, ethyl 2-bromoisobutyrate (EBiB) was used as the oil-soluble initiator. Several surfactants with a large range of hydrophile-lypophile balance (HLB) values were tested. The critical micellar concentration (emc) and the pH of the medium were also measured to determine their effects on the emulsion stability. The direct ATRP most likely proceeds via the suspension mechanism. In reverse ATRP, 2,2'-azobis[2-(2-dimidazolin-2-yl)propane] dihydrochloride (VA-044) was used as the water-soluble initiator, and the results suggest an emulsion polymerization mechanism. In both approaches, the kinetics were followed along with the particle size (measured by laser diffraction and SEM), and the influence of the halogen atom associated with the catalyst (i.e., CuBr or CuCl) was examined. It was demonstrated that utilizing the halide exchange could improve the control over both the molecular weight and end functionality of the polymers.