This User's Guide is a comprehensive manual for persons accessing the 1978 version of National Fire Danger Rating System on AFFIRMS. AFFIRMS, the Administrative and Forest Fire Information Retrieval and Management System is a user-oriented, interactive computer program. Weather observations and fuels data are processed to produce a rating of probable forest fire danger in the form of fire danger indexes. Fuels and weather data are also automatically checked for errors and archived. Other program output includes narrative messages sent between users, and observed and forecasted weather. This version of the User's Guide to AFFIRMS supercedes the August 1975 version published as USDA Forest Service General Technical Report RM-15. The Guide is written in nontechnical language for persons without a computer background.