  Rotation has a number of important effects on the evolution of stars. Apart
from structural changes because of the centrifugal force, turbulent mixing and
meridional circulation caused by rotation can dramatically affect a star's
chemical evolution. This leads to changes in the surface temperature and
luminosity as well as modifying its lifetime. Observationally rotation
decreases the surface gravity, causes enhanced mass loss and leads to surface
abundance anomalies of various chemical isotopes. The replication of these
physical effects with simple stellar evolution models is very difficult and has
resulted in the use of numerous different formulations to describe the physics.
Using stellar evolution calculations based on several physical models we
discuss the features of the resulting simulated stellar populations which can
help to distinguish between the models.
