CH4 is an important greenhouse gas and also a precursor of the air pollutant O3. About 60% of the current global methane is emitted by sources like agriculture, landfills and wastewater, and the production and pipeline transport of fossil fuels, while ca. 40 % is from natural sources. At world level, CH4 emissions and concentrations are still increasing, raising concerns for air quality and climate change. This study, building on evidence from observations and modelling, suggests that CH4 emission reductions can play a key-role in further reducing O3 in Europe and in the world. Since Europe’s contribution to global CH4 emissions is currently only about 6 %, global cooperation to reduce CH4 in countries and regions in- and outside of the EU, will also be essential to reduce related O3 effects in Europe and the world.