The ISV (Imposto Sobre Veiculos) is a registration tax that is only paid once when the vehicle is first registered in Portugal.
ISV is calculated on the basis of two criteria: the engine cubic capacity and CO2 emissions. Some types of vehicles, such as commercial and motorcycles, pay ISV based on the engine feature only.
In Portugal, there are no taxes for buying an used car - only pay the registration fee. There are no regional taxes too.
All-electric vehicles do not pay ISV nor IUC (Imposto Único Circulação / circulation tax).