  We address the global magnetic phase diagram of Kondo lattice systems.
Through the distinct Fermi surface properties of the various phases at zero
temperature, we argue that the phase diagram supports two classes of quantum
critical point. One of these describes a direct transition from a magnetic
metal phase with localized f-electrons to a paramagnetic one with itinerant
f-electrons. This result provides the context for the picture of local quantum
criticality, in which the Fermi surface jumps across the quantum critical point
and the quasiparticle residue vanishes as the quantum critical point is
approached from either side. Some of the unusual experiments, concerning the
phases and quantum critical points of heavy fermion metals, are discussed from
the present perspective. These developments have implications in broader
contexts. In particular, they form a part of the growing evidence for quantum
criticality that goes beyond the orthodox description in terms of
order-parameter fluctuations.
