I consider some selected topics in chiral perturbation theory (CHPT) as probed at colliders such as DA$\Phi$NE. Emphasis is put on processes involving pions in the isospin zero S-wave which require multi-loop calculations. These include the scalar form factor of the pion, two--photon fusion into pion pairs and $K_{ \ell 4}$--decays. The physics of the chiral anomaly is briefly touched upon
Categories: hep-ph nucl-th