  Unusual properties of strongly correlated liquid observed in the high-$T_c$
superconductors and heavy-fermion (HF) metals are determined by quantum phase
transitions taking place at their critical points. Therefore, direct
experimental studies of these transitions and critical points are of crucial
importance for understanding the physics of high-$T_c$ superconductors and HF
metals. In case of high-$T_c$ superconductors such direct experimental studies
are absent since at low temperatures corresponding critical points are occupied
by the superconductivity. Recent experimental data on the behavior of HF metals
illuminate both the nature of these critical points and the nature of the phase
transitions. We show that it is of crucial importance to simultaneously carry
out studies of both the high-$T_c$ superconductivity and the anomalous behavior
of HF metals. Our general consideration suggests that FCQPT and the emergence
of novel quasiparticles near and behind FCQPT are distinctive features of
strongly correlated substances such as the high-$T_c$ superconductors and HF
metals. We show that the main properties and universal behavior of the
high-$T_c$ superconductors and HF metals can be understood within the framework
of presented here theory based on FCQPT. A large number of the experimental
evidences in favor of the existence of FCQPT in high-$T_c$ superconductors and
HF metals is presented.
