Improving the charge carrier mobility of solution-processable organic semiconductors is critical for the development of advanced organic thin-film transistor (OTFTs) and their application in the emerging sector of printed electronics. To this end, molecular doping can be seen as a powerful tool with the potential to resolve many of the outstanding issues that are currently preventing OTFT commercialisation. Yet the addition of dopant molecules into an organic semiconductor often disrupts its microstructure, introducing defects and therefore harming long-range charge transport. In this presentation I will discuss different doping methods that can be used to enhance the charge carrier mobility in OTFTs based on a wide range of organic semiconductors including, small-molecules, polymers and small-molecule:polymer blends, with the latter system exhibiting the most promising performance characteristics. Emphasis will be placed on the “all-round” positive effect that the inclusion of a suitable dopant has on key OTFT characteristics including contact resistance, bias-stress stability and device-to-device parameter variation.