  We demonstrate that, together with the available experimental information,
chiral symmetry determines the low energy behaviour of the $\pi\pi$ scattering
amplitude to within very small uncertainties. In particular, the threshold
parameters of the S-, P-, D- and F-waves are predicted, as well as the mass and
width of the $\rho$ and of the broad bump in the S-wave. The implications for
the coupling constants that occur in the effective Lagrangian beyond leading
order and also show up in other processes, are discussed. Also, we analyze the
dependence of various observables on the mass of the two lightest quarks in
some detail, in view of the extrapolations required to reach the small physical
masses on the lattice. The analysis relies on the standard hypothesis,
according to which the quark condensate is the leading order parameter of the
spontaneously broken symmetry. Our results provide the basis for an
experimental test of this hypothesis, in particular in the framework of the
ongoing DIRAC experiment: The prediction for the lifetime of the ground state
of a $\pi^+\pi^-$ atom reads $\tau=(2.90\pm 0.10)10^{-15} sec$.
