The silicone rubbers are classified according to the different vulcanization ( RTV1, RTV2, HTV, LSR). Based on the chemistry of reactions the vulcanization (condensation, radical und addition curing) is described including main components and byproducts. The different reactivity and the resulting set up for the process parameters are explained. The type of vulcanization influences also the properties of the cured end product and their acceptance for different end uses like industrial, food contact and medical applications.