Volume I describes the Industrial Source Complex Dispersion Model and its use. The model updates various EPA dispersion model algorithms and combines them in two computer programs that can be used to assess the air quality impact of emissions from the wide variety of source types associated with an industrial source complex. The ISC Model short-term program ISCST, an updated version of the CRSTER, uses sequential hourly meteorological data to calculate values of average concentration or total dry deposition for time periods of 1, 2, 3, 4, 6, 8, 12 and 24 hours. Additionally, ISCST may be used to calculate 'N' is 366 days. The ISC Model long-term computer program ISCLT, a sector-averaged model that updates and combines basic features of the Air Quality Display Model AQDM and the Climatological Dispersion Model CDM, uses STAR summaries to calculate seasonal and/or annual average concentration or total deposition values. The ISC Model programs are written in Fortran IV for the Univac 1110 computer. The two programs may also be used on medium-to-large IBM or CDC computer systems with little or no modification.