For many years, considerable research efforts have been dedicated to pi-conjugated polymers because of their extraordinary electronic, optical, and structural properties. The employed transition-metal-based initiating systems comprise not only simple transition-metal salts but also rather sophisticated Mixtures of two, three, or four compounds and even highly defined single-component systems such as transition-metal alkylidene complexes. Extensive fine-tuning of the electronic and steric properties of initiator-monomer systems eventually allowed the tailor-made synthesis of conjugated materials via living polymerization techniques. This article focuses on recent developments in the field of the living polymerization of substituted acetylene derivatives. Ill-defined group 5 and 6 transition metal halide-based initiators, well-defined transition-metal alkylidene complexes, and rhodium(I)-based systems that induce the living polymerization of numerous substituted acetylenes are reviewed. (c) 2005 Wiley Periodicals, Inc.