An official Memorandum of Understanding among the United States Environmental Protection Agency (EPA), the United States Department of Agriculture Forest Service, National Park Service, and the U.S. Fish and Wildlife Service was signed and completed November 25, 1991. As part of that agreement, an Interagency Work Group for Air Quality Modeling (IWAQM) was formed. IWAQM had a special version of the CALPUFF Modeling System prepared in their efforts to review, identify, and recommend candidate air quality modeling techniques that can be used to estimate pollution concentrations on a regional scale, with emphasis on Federal class 1 areas. The CALPUFF Modeling System is composed of three basic components; CALMET, CALPUFF, and CALPOST. CALMET is a meteorological processor which was modified to enable use of vertical profiles of wind and temperature as characterized by the MM4-FDDA (Mesoscale Model-4 with Four-Dimensional Data Assimilation) meteorological model CALPUFF is a Lagrangian puff dispersion model and CALPOST is a postprocessor program that has been modified for ease of use and interpretation. CALPOST was modified to include a light extinction algorithm for use in regional visibility impact assessments. The CALPUFF Modeling System CD-ROM contains the versions of the models that were current in December 1994 as well as sample input data and batch files for model demonstration runs, the output files produced by the demonstration runs, and databases of general utility. The databases on the CD-ROM contain terrain elevations and land-use data for the contiguous United States. MM4-FDDA meteorological wind and temperature fields at an 80-km resolution are also provided for the time period (1983) of the Cross-Appalachian Tracer Experiment (CAPTEX).