Abstract Molecular doping of organic semiconductors has been widely utilized to modulate the charge transport characteristics and charge carrier concentration of active materials for organic electronics such as organic photovoltaics, organic light-emitting diodes, and organic field-effect transistors. For the application of molecular doping to organic electronics, the fundamentals of molecular doping should be thoroughly understood in terms of doping mechanism, host and dopant materials, doping methodologies, and post-doping properties such as doping-induced structural/energetic disorder and doping stability. In this report, the fundamental understanding of molecular doping, types of dopants, doping methods, and their practical applications as organic field-effect transistors, organic photovoltaics, and organic thermoelectric are reviewed. Finally, key strategies for efficient molecular doping may exceed the trade-off relation between device performance and structural disorder.