Final State Interactions in 3-body decay: challenges and future

Three-body hadronic decays of B and D mesons are a superb laboratory for studying Charge-Parity (CP) violation and hadronic Final states Interactions. The gigantic samples of B and D decays collected by the LHCb (and more to come from others) experiments motivated theoretical efforts in the past decade towards building models that are based on more solid grounds. I presented an overview of these models. In particular, interesting results one obtain for $B^+ \to \pi^-\pi^+\pi^+$ with novel mechanisms of the CP asymmetries pattern observed in the Dalitz plot.