Chiral perturbation theory at two loops and the measurement of V(us)
I give an overview of the calculations done in three-flavour Chiral perturbation theory at next-to-next-to-leading order with an emphasis on those relevant for an improvement in the accuracy of the measurement of Vus. It is pointed out that all needed low energy constants can be obtained from experiment via the scalar form-factor in Kl3 decays
