Because silicon is abundant in the Earth's crust and its compounds are considered less toxic, using silicon compounds as catalysts has been attractive for organic chemists. However, despite its high potential silicon catalysis had been limited to conventional tetravalent silicon Lewis acids such as Me3SiOTf. Recent discoveries of highly active silylium ion and neutral silicon catalysts have now been accelerating the development of silicon catalysis. This chapter summarises the progress of conventional and new silicon-based catalysts.