Controlled radical polymerization (CRP), sometimes also termed ?living' radical polymerization, offers the potential to create a wide range of polymer architectures, and its implementation in aqueous dispersed media (e.g. emulsion polymerization, used on a vast scale industrially) opens the way to large-scale manufacture of products based on this technique. Until recently, implementing CRP in aqueous dispersed media was plagued with problems such as loss of ?living' character and loss of colloidal stability. This review examines the basic mechanistic processes in free-radical polymerization in aqueous dispersed media (e.g. emulsion polymerization), and then examines, through this mechanistic understanding, the new techniques that have been developed over the last few years to implement CRP successfully in emulsion polymerizations and related processes. The strategies leading to these successes can thus be understood in terms of the various mechanisms which dominate CRP systems in dispersed media; these mechanisms are sometimes quite different from those in conventional free-radical polymerization in these media.