Flavour physics within and beyond the Standard Model

— I review recent progress in theoretical calculations related to the CKM unitarity triangle. After briefly discussing hints for new physics in Bd−Bd and Bs−Bs mixing I present three topics of MSSM flavour physics: First I discuss new tanβ-enhanced radiative corrections to flavour-changing neutral current (FCNC) amplitudes which go beyond the familiar Higgs-mediated FCNC diagrams and may enhance the mixing-induced CP asymmetry in Bd → φKS. The second topic is a reappraisal of the idea that flavour violation originates from the soft supersymmetrybreaking terms. Finally I discuss how μ → eγ can be used to constrain the flavour structure of the dimension-5 Yukawa interactions which appear in realistic grand unified theories.