This guide provides detailed information about the EU Emissions Trading System (EU ETS), including information about how the system was designed and how it operates. This document is aimed at those who want to understand the EU ETS. Although it has been written for non-experts, this guide does not provide the underlying theory of market-based instruments and emissions trading systems in general. Some prior basic knowledge of the principles of an emissions trading system would be helpful when using this manual. (see e.g. Hansjèurgens (2010), “Emissions Trading for Climate Policy” or Ellerman et al. (2010), “Pricing Carbon: The European Union Emissions Trading Scheme”).