Chiral dynamics in the meson sector at two loops
I give a very short introduction to chiral perturbation theory and an overview of the next-to-next-to-leading order three-flavour calculations done. I discuss those relevant for an improvement in the accuracy of the measurement of Vus in more detail. One major conclusion is that all needed p6 low energy constants can be obtained from experiment via the scalar form-factor in Kl3 decays