The report empirically investigates the causal effects of three decisions adopted by the European Commission on the performance of telecoms markets, namely the T-Mobile/Orange merger in the UK mobile markets, a state aid decision in the German fixed broadband market and an abuse of dominant position by Telekomunikacja Polska in the Polish fixed market. The report also provides a descriptive analysis on the evolution of competition policy enforcement in the telecoms markets and the concurrent trends in markets’ performance.