  The original canonical coherent states could be defined in several ways. As
applications for other sets of coherent states arose, the rules of definition
were correspondingly changed. Among such rule changes were a change of group
and relaxation of the analytic nature of the labels. Recent developments have
done away with the group connections altogether and thereby allowed sets of
coherent states to be defined that are temporally stable for a wide variety of
dynamical systems including the hydrogen atom. This article outlines some of
the current trends in the definitions and properties of present-day coherent
states.
