A program for the generation of high-energy physics events. The simulation of events as they will take place in the Atlas detector, starts with the simulation of the collisions themselves. This is done in event generators such as HERWIG, a Monte Carlo package for simulating Hadron Emission Reactions With Interfering Gluons, which contains theory and models for e.g. hard and soft interactions, parton distributions, initial and final state parton showers, particle decay, etc. The output of an event generator can subsequently be fed into the Atlas detector simulation, which tracks the particles from the events through Atlas. Detailed information is available on the HERWIG site. There is also Atlas specific information, which describes the Herwig_i interface package for use with ATHENA. See Also JIMMY.