The European Union is running the largest multi-country, multi-sector greenhouse gas emission trading scheme (ETS) world-wide. This report presents the experiences from Member States on the implementation of the trading system. The report for reporting year 2008 covers both specific information on the trading year 2007 as well as some findings from the whole first trading period. The report also contains a short discussion around the risk of carbon leakage. Over the course of the three-year period, increasing knowledge was collected on key figures and experience gained in implementing the Emissions Trading Scheme. A number of lessons were learned that have reshaped the design and implementation of the system and will continue to do so. The report reveals that there is still room for further alignments, which to a certain degree already have been addressed. From the trading year 2008 a new version of guidelines on monitoring and reporting is applied. Some other issues are addressed in the proposed amendment of the Trading Directive that is under discussion in the Council and the European parliament.