  We review the empirical scenario emerging from the measured doping dependence
of the transition temperature and the anisotropy parameter $% \gamma $ $=\xi
_{ab}/\xi_{c}$, defined as the ratio of the correlation lengths parallel and
perpendicular to the ab-planes. It suggests that two dimensional models cannot
explain the occurrence of superconductivity in the cuprates. This conclusion is
confirmed and extended in terms of a novel scaling relation. It involves the
transition temperature, the aerial superfluid density in the ground state,
$\gamma $ and the dynamic critical exponent of the quantum superconductor to
insulator transition. The important implication there is that a non vanishing
superfluid density in the ground state of the cuprates is unalterably linked to
an anisotropic but 3D condensation mechanism.
