  I review our incomplete understanding of non-Fermi liquid behavior in heavy
fermion systems at a quantum critical point. General considerations suggest
that critical antiferromagnetic fluctuations do not destroy the Fermi surface
by scattering the heavy electrons- but by actually breaking up the internal
structure of the heavy fermion. I contrast the weak, and strong-coupling view
of the quantum phase transition, emphasizing puzzles and questions that recent
experiments raise.
