  To provide an understanding of the universal thermodynamic properties of
cuprate superconductors, emerging from the empirical correlations and phase
diagrams, we analyze them in terms of the scaling theory of finite temperature
and quantum critical phenomena. The universal features are traced back to the
existence of quantum critical lines, representing the end lines of the finite
temperature transition surface. At the respective quantum critical lines two
dimensional superconductor to insulator (2D-QSI) transitions and three
dimensional superconductor to normal state (3D-QSN) transitions occur. The flow
to this quantum critical points is tuned by doping, substitution and
anisotropy. It is shown that the empirical correlations, like the dependence of
$T_{c}$on dopant and substitution concentration, the dependence of $T_{c}$ on
zero temperature in-plane penetration depth, etc., as well as the anomalous
isotope effect on $T_{c}$ and penetration depth, reflect the universal
properties associated with the flow to these quantum critical points and of the
crossover from one to the other.
