  The map between the moduli space of F-theory (or type II string)
compactifications and heterotic string compactifications can be considerably
simplified by using "stable degenerations". We discuss how this method applies
to both the E8 x E8 and the Spin(32)/Z2 heterotic string. As a simple
application of this method we derive some basic properties of the
nonperturbative physics of collections of E8 or Spin(32)/Z2 point-like
instantons sitting at A-D-E singularities on a K3 surface.
