  HERWIG (Hadron Emission Reactions With Interfering Gluons) is a multipurpose
Monte Carlo event generator for the simulation of hard collisions between
hadrons, leptons and photons. This note describes the new features of version
5.9. These include adding over 100 new particles, 1800 new decay modes and
supporting new decay types. A complete space-time picture, including heavy
meson mixing and secondary decays, is available for all event types and
includes an optional colour rearrangement model. Initial state radition of
photons in e^+e^- is is now included. Many other processes and features have
been upgraded.
