It is a basic property of the entropy in statistical physics that is concave
as a function of energy. The analog of this in representation theory would be
the concavity of the logarithm of the multiplicity of an irreducible
representation as a function of its highest weight. We discuss various
situations where such concavity can be established or reasonably conjectured
and consider some implications of this concavity. These are rather informal
notes based on a number of talks I gave on the subject, in particular, at the
1997 International Press lectures at UC Irvine.