Polythiophene synthesis has undergone a multitude of changes, starting from the initial methods of acid-catalyzed polymerizations with low yields of oligomeric polythiophenes to modern methods using transition metal-based catalysts that allow controlled synthesis of poly(alkylthiophene)s with high molecular weight and regioregularity. The discovery of the opto-electronic properties of conjugated polymers played a major role in this development. Further improvements such as externally initiated polymerization not only enabled the synthesis of polymers that are almost 100% regioregular, but also gave the capability for in situ synthesis of these polymers on substrates, which increases their applicability in opto-electronic devices. This chapter summarizes developments in the methodology of polythiophene synthesis.