This paper provides an introduction to the EU’s Emissions Trading System. As such it provides a discussion of the historical and legal context in which the EU ETS developed and now operates, a presentation of the key performance indicators for the first eight years through the end of the second phase in 2012, and some concluding observations on the system’s future. The paper is purposively descriptive to provide background for more analytically oriented articles, as well as to provide a matter-of-fact presentation for readers who wish to learn about or be updated on the progress of the EU ETS.