In the last years, the NA48/2 experiment at the CERN SPS has recorded an unprecedented sample of charged kaon decays. From this, we report several very precise measurements of fundamental parameters of Chiral Perturbation Theory (ChPT). Several rare and very rare decays have been studied. From more than $10^6$ $K^{\pm}$ decays to charged pion, Pi0, and gamma decays, a first measurement of the interference between Bremsstrahlung and Direct Emission amplitudes and a stringent limit on direct CP violation in this channel is presented. For $K+- \rightarrow$ pi+ gamma gamma, about 1000 events have been selected, more than 30 times the existing statistics. Also, the first observation of $K+- \rightarrow$ pi+ gamma e+ e- is reported with 120 events. For both decays, the branching fraction and the free parameter of O(p$^4$) ChPT has been measured with high accuracy. Finally, we report on a new precise measurement of the branching fraction and form factors of K+- -> pi+- e+ e-, which is highly suppressed by the GIM mechanism. The measurement of the e+ e- spectrum is an important input for ChPT and probes the weak static interaction. Results from other experiments on this field will be summarized.