This article examines the making and implementation of the 2009 European Union (EU) regulation on cars and CO2 emissions (Regulation [EC] No 443/2009). As the first legally binding measure to target the CO2 emissions of passenger cars, this regulation represents a milestone in EU efforts to reduce the climate impacts of road transport. The analysis draws on two central theoretical perspectives on EU policy making: liberal intergovernmentalism and supranationalism. Both offer important insights, but their explanatory power varies with the policy-making phase in focus. The analysis shows that the Commission and the car industry were instrumental in shaping what eventually became an industry-friendly regulation applicable in all EU countries. However, far from being a case of closed negotiations between the industry and the Commission, Germany and other EU countries defending the interest of manufacturers of high-emission vehicles made use of their powers during the decision-making phase and succeeded in watering down the Commission's proposal.