Though codified as appendix W in July 1993, the Guideline on Air Quality Models (``Guideline'') had never been properly organized to conform with the CFR format (which features sequentially numbered paragraphs) imposed by the Office of the Federal Register. Thus, this direct final rule republishes the Guideline to reflect the format appropriate for appendix W. In addition, reference lists are alphabetized and updated, technical contacts and availability for models are updated, and typographical errors are corrected. Two new models presented at the 6th Conference on Air Quality Modeling (August 1995) are added to Guideline appendix B for case-by-case use; several outdated models are removed from appendix B. Appendix A models considered to be ``obsolete'' (i.e., CRSTER & MPTER, replaced by ISC3) are removed, as is Table 4-1. In addition, minor amendments to 40 CFR 51.112, 51.160. 51.166, and 52.21 are necessary to bring respective references to appendix W up to date.