Michel Henon's contributions to collisional stellar systems
  The theory of star cluster dynamics was a major topic in H\'enon's early
research career. Here we summarise his contributions under three headings: (i)
the Monte Carlo method, (ii) homological evolution of star clusters, and (iii)
escape from star clusters. In each case we also trace some aspects of how
H\'enon's contributions have been developed or applied in subsequent decades up
to the present. We also propose that H\'enon's work be commemorated by adopting
the names "H\'enon units" and "H\'enon's Principle".
