The Supreme Court ruling in Massachusetts v. EPA, 549 U.S. 497 (2007) that determined that greenhouse gases (GHGs) including carbon dioxide (CO2) are air pollutants covered by the Clean Air Act (CAA). The Environmental Protection Agency (EPA) has begun to issue rules that either collect on or control the emission of GHG from large sources. This paper summarizes the implications of the following EPA rules on owners of publically-owned treatment works (POTWs): • October 30, 2009, 74 FR 56260; “Mandatory Reporting of Greenhouse Gases” (the “Reporting Rule”) • December 15, 2009, 74 FR 66496; “Endangerment and Cause or Contribute Findings for GHGs under Section 202(a) of the CAA” (the “Endangerment Finding”) • June 3, 2010, 75 FR 31514; “Prevention of Significant Deterioration and Title V Greenhouse Gas Tailoring Rule” (the “Tailoring Rule”) • January 12, 2011, “GHG Permitting Requirement Deferral for Industries that Use Biomass”