With the EU ETS 2 a new EU-wide emissions trading system is introduced that covers the greenhouse gas emission of the buildings and road transport sectors, i.e. sectors the decarbonization of which has so far been the responsibility of the Member States under the Effort Sharing Regulation. Since they will remain responsible for the achievement of their national greenhouse gas emission reduction targets under that regime, the question arises whether the Member States can maintain or introduce additional carbon pricing instruments alongside the new EU ETS 2. Hence, this paper examines the legality of such an approach, by assessing relevant provisions of EU secondary and primary law. Without going deep into the economic and political considerations, it concludes that from a legal perspective, the coexistence of national carbon pricing instruments and the EU ETS 2 is not prohibited.With the latest reform of the EU Emissions Trading System Directive (ETS Directive), the European Union (EU) has introduced a new EU emissions trading system for buildings and road transport (EU ETS 2)1. The decarbonization of those sectors traditionally falls within the responsibility of the EU Member States under the regime of the Effort Sharing Regulation (ESR). The ESR introduces legally binding national greenhouse gas (GHG) emission reduction targets. Hence, over the last few years, the Member States have introduced different measures in order to reach their targets. Those include carbon pricing instruments, understood as measures that put a price on the emission of GHG and thus create an incentive to reduce those emissions. Carbon pricing instruments include carbon taxes, as well as emissions trading systems2. With the introduction of the new ETS 2, the question arises whether the Member States can maintain (or introduce) such national carbon pricing instruments in parallel to the new EU ETS 2.