2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/200665This talks contains a short introduction to Chiral Perturbation Theory and the existing calculations to two-loop order in the mesonic sector. I include a discussion on which quantities the expansion can be organized in. The present best values of the Low-Energy-Constants as determined from continuum physics are given as well as the assumptions underlying the fits to experimental data. I present plots of masses, decay constants and $f_+(0)$ in $K_{\ell3}$ as a function of quark or meson masses. The talk ends with a list of things for which it would be extremely useful to have good results from lattice QCD calculations.15 pages, plenary talk at T he XXV International Symposium on Lattice Field Theory, July 30 - August 4 2007, Regensburg, Germany. v2: some clarifying statements addedHigh Energy Physics - LatticeHigh Energy Physics - Phenomenologytext