This article explores the causes for differences in the average CO2 emissions intensity of the new passenger car (NPC) fleet in member states (MS) across Europe. Although EU policies mitigating CO2 emissions from NPCs have been in place since 1999, MS strongly diverge in the absolute amount and relative change in emissions over the last decade. The authors employ a qualitative approach to analyse the factors, in particular national vehicle taxes, contributing to this divergence and the relative contribution of national and European policies in reducing national CO2 emissions from NPCs. The analysis shows that there has been a significant reduction in CO2 emissions intensity of NPCs since 2007 across most MS, compared with the six years previous to that date. This would indicate that EU-wide policies, such as the CO2 vehicles regulation, along with the economic recession in 2008, have influenced national NPC CO2 emissions. Generally, countries with CO2-differentiated vehicle taxes are observed as more likely to have achieved greater reductions in CO2 emissions. However, over the same period there have been many confounding factors, such as economic instability in the EU, that also influence NPC emissions. Using more detailed case study analyses of six countries, the authors find that there is scope for well-designed national vehicle tax policies to drive NPC emissions down further than the EU average. In countries with the highest success rate, such as the Netherlands, the design of the vehicle tax, as part of a well-aligned policy package, has been very important in delivering the biggest reductions in CO2 emissions from NPCs.POLICY RELEVANCEThe transport sector continues to be an intractable source of CO2 emissions. Governments around the world are seeking effective policies to deal with the increase in passenger car CO2 emissions appropriate to their own circumstances. This article examines the experience of EU MS with CO2-differentiated vehicle taxes in reducing CO2 emissions in the context of other national and international contributing factors. It should therefore both be useful to policy makers and contribute to climate policy research in general.