  We find low energy equivalences between $N=2$ supersymmetric gauge theories
with different simple gauge groups with and without matter. We give a
construction of equivalences based on subgroups and find all examples with
maximal simple subgroups. This is used to solve some theories with exceptional
gauge groups $G_2$ and $F_4$. We are also able to solve an $E_6$ theory on a
codimension one submanifold of its moduli space.
