  The all--important consequence of Chiral Dynamics for $\pi \pi$ scattering is
the Adler zero, which forces $\pi \pi$ amplitudes to grow asymptotically. The
continuation of this subthreshold zero into the physical regions requires a
$P$--wave resonance, to be identified with the $\rho$. It is a feature of $\pi
\pi$ scattering that convergent dispersive integrals for the $I=1$ channel are
essentially saturated by the $\rho$--resonance and are much larger than those
with $I=2$ quantum numbers. These facts predict the parameters
$\overline{\ell}_1$, $\overline{\ell}_2$ of the Gasser--Leutwyler Chiral
Lagrangian, as well as reproducing the well--known KSFR relation and
self-consistently generating the $\rho-$resonance.
