For the last 15 years the European Union (EU) has been particularly active, both internally and internationally, in the fight against global warming, and it is determined to continue to play a global leadership role in this strategic issue. Among the various market-based measures decided upon, the Emission Trading Scheme (ETS) for energy-intensive industrial sectors has been rightly described as the ‘flagship of the EU climate policy’.1 Even before proceeding to a general overhauling of Directive 2003/87 in the framework of the 2009 Climate and Energy package, the EU had decided to modify the Directive by including aviation activities in the ETS. Directive 2008/1012 provides that all flights from whichever aircraft operator taking off from or landing in the EU territory will be subjected to the ETS from 1 January 2012. For the year 2012 97 per cent of all emissions allowances will be freely assigned, from 2013 the amount will decrease to 95 per cent, whereas 15 per cent of all allowances will be auctioned. In reality the percentage of free allowances is much lower, about 60 per cent, because it takes as parameter the historical aviation emissions of the years 2004–06, when the air traffic was 40 per cent lower than it is now. The idea underlying the Directive is that aircraft operators will either purchase the necessary allowances in the market or will try to reduce their emissions by using bio-fuels (or else reducing the number of flights), with the second option becoming more economically attractive over time.