EPA is issuing this guidance document to assist permit writers and permit applicants in addressing the prevention of significant deterioration (PSD) and title V permitting requirements1 for greenhouse gases (GHGs) that begin to apply on January 2, 2011. This document: 1. describes, in general terms and through examples, the requirements of the PSD and title V permit regulations; 2. reiterates and emphasizes relevant past EPA guidance on the PSD and title V review processes for other regulated air pollutants; 2 and 3. provides additional recommendations and suggested methods for meeting the permitting requirements for GHGs, which are illustrated in many cases by examples. We believe this guidance is necessary to respond to inquiries from permitting authorities and other stakeholders regarding how these permitting programs will apply to greenhouse gas (GHG) emissions. This document is organized into sections with supporting appendices. Section I describes the purpose of this document, describes the actions that led to the permitting of sources of GHGs, and provides a general background for the permitting of major stationary sources. Section II describes PSD applicability criteria and how to determine if a proposed new or modified stationary source is required to obtain a PSD permit for GHGs. Section III discusses the process that EPA recommends following to determine best available control technology (BACT) for GHGs for new sources and modified emissions units. Section IV discusses how other PSD permitting requirements are generally inapplicable or have limited relevance to GHGs. Section V describes considerations for permitting of GHGs under title V of the Clean Air Act (CAA or Act). The appendices located at the end of this document include PSD applicability flowcharts for new and modified sources of GHGs, an example PSD applicability analysis for a modified source, example BACT analyses, compilations of resources for estimating emissions of GHGs and for finding control measures for sources of GHGs, and cost effectiveness calculation methodology.