Comprehensive review of the state and trends of the carbon market as of May 2005, based on material provided by Natsource and Evolution Markets, and on direct interviews with market participants. The paper provides an overview of the main segments of this market, and how they inter-relate. It covers both the generation of GHG emissions reductions through project-based transactions and the trading of GHG emissions allowances under cap and trade schemes like the EU ETS. The paper concludes with a discussion of the major trends emerging in the GHG market.