Flavour-Changing-Neutral currents provide stringent tests of the Standard
Model and of extensions of it that feature new sources of flavour violation.
To take advantage of the ongoing and planned experimental program requires
precision predictions within effective theories but also new ways to interpret
and search for possible deviation in flavour data. In this talk we focus on
observables from the Kaon and Bottom sector, discuss the challenges and recent
developments in their predictions, and investigate the possibility of using
them to probe lepton-number-violation and light New Physics scenarios.