  Kaon flavour physics has played in the 1960s and 1970s a very important role
in the construction of the Standard Model (SM) and in the 1980s and 1990s in SM
tests with the help of CP violation in $K_L\to\pi\pi$ decays represented by
$\varepsilon_K$ and the ratio $\varepsilon'/\varepsilon$. In this millennium
this role has been taken over by $B_{s,d}$ and $D$ mesons. However there is no
doubt that in the coming years we will witness the return of kaon flavour
physics with the highlights being the measurements of the theoretically clean
branching ratios for the rare decays $K^+\rightarrow \pi^+\nu\bar\nu$ and
$K_{L}\rightarrow\pi^0\nu\bar\nu$ and the improved SM predictions for the ratio
$\varepsilon'/\varepsilon$, for $\varepsilon_K$ and the $K^0-\bar K^0$ mixing
mass difference $\Delta M_K$. Theoretical progress on the decays
$K_{L,S}\to\mu^+\mu^-$ and $K_L\to\pi^0\ell^+\ell^-$ is also expected. They all
are very sensitive to new physics (NP) contributions and the correlations
between them should help us to identify new dynamics at very short distance
scales. These studies will be enriched when theory on the $K\to\pi\pi$ isospin
amplitudes ${\rm Re} A_0$ and ${\rm Re} A_2$ improves. This talk summarizes
several aspects of this exciting field. In particular we emphasize the role of
the Dual QCD approach in getting the insight into the numerical Lattice QCD
results on $K^0-\bar K^0$ mixing and $K\to\pi\pi$ decays.
