Today's market increasingly demands sophisticated materials for advanced technologies and high-value applications, such as nanocomposites, optoelectronic, or biomedical materials. Therefore, the demand for well-defined polymers with very specific molecular architecture and properties increases. Until recently, these kinds of polymers could only be prepared via living ionic polymerization, a process that requires very stringent experimental conditions. Recently, atom transfer radical polymerization (ATRP), a controlled/living radical polymerization (CRP) process, has emerged as a viable alternative. ATRP allows the synthesis of polymeric structures that are well-defined in terms of composition and molecular architecture. By virtue of its simplicity, versatility and scope to make polymers with site-specific functionality and novel architecture, ATRP has become the most extensively studied CRP technique. (Contains 1 figure and 5 schemes.)