  We report on our recent results in the study of the chiral extrapolation of
the phase-shifts in elastic pion-pion scattering, using both standard and
unitarized ChPT to one and two loops. In the standard ChPT approach, limited to
low momenta, we study the S, P and D waves. Unitarization extends the analysis
to energies of around 1 GeV, being compatible with standard ChPT at low
energies for the S and P waves. We then compare with lattice results and find a
good agreement of standard ChPT below p \sim 200 MeV for the I=2, J=0 and I=1,
J=1 channels and up to p \sim 500 MeV for the I=2, J=2 channel. Unitarized ChPT
improves the agreement in the scalar and vector channels at higher energies. We
have also performed a Montecarlo analysis to provide an estimation of the
uncertainties.
